FUNDAMENTS OF DESIGN OF
FABRICS AND GARMENTS WITH
DEMANDED
THERMOPHYSIOLOGICAL COMFORT
by Prof. Lubos Hes, PhD., DSc,
University of Liberec, Czech Republic,
e-mail: luboshes@vslib.cz
1.HIGH ADDED VALUE CLOTHING AND
GARMENTS DESIGNED BY THE APPLI CATION OF
COMFORT SCIENCES
Due to increasing sales of functional and
protective clothing, clothing comfort and the
related evaluation methods became very important
in recent years.
Comfort perceived by human senses: eyes, ears,
touch, nose.
Comfort defined as the absence of perceived painand discomfort. A new concept of garments with
defined, but not maximal comfort level for young
healthy people, sportsmen under training scheme
etc.
1.1. Components of clothing comfort:
psychological, sensorial (or tactile) and
thermophysiological comfort.
2. PSYCHOLOGICAL COMFORT: geographical
(climatic), economical, hi-storical, cultural, social
and individual aspects.
2.1.Components of psychological comfort
Climatic aspects: typical (daily) clothing should at
first respect the climatic requirements
Economical aspects: Resources, technology of
food and objects manu-facture, skills, political
system
Historical aspects: Inclination to products made of
natural materials, to products simulating nature, to
products of natural smell. Tradition in lifestyle and
fashion
Cultural aspects: religion, habits (in Arabic
countries women are fully covered)
Social aspects: age, qualification, social class,
rank or position in this class
Individual and group aspects: the effect of fashion,
style, colours and lustre, trends, personal
preferences
3.SENSORIAL COMFORT
3.1.Stephen's law, skin sensors: perceived
sensation P (sound, lightning, climate) is
proportional to the magnitude of physical stimulus
I according to the relation:
P = d In
Skin temperature (Kraus & Ruffini) sensors:
sensors for 38 to 43OC, cold sensors for 15 to
35OC, low sensitivity between 35 and 38OC.
Adaptability with acclimatisation.
(1)
Sensors for pressure and pain. No sensor for
humidity (substituted by feeling of cold and
pressure).
Fig. 1 Schematic section view of human skin
1)Hair sheath
2)Hair
3)Smooth muscles
4)Fat gland
5)Skin vein
6)Sweat gland
7)Touch sensor
8)Higher temperature sensor by Ruffini
9)Vater-Paccini sensor of pressure and pull
10)Lower temperature sensor by Krause
11)Free ends of nerves
3.1.1.Sensory properties of fabrics and their
division into mechanical, thermal and complex
properties. Dynamic (Newton) force F [N/m2]given
by acceleration a [m/s2] of a fabric mass m [kg/m2]:
F
=
m
.
a
(2)
and friction forces generated while wearing
clothing. Ergonomic approach to garment design.
3.2.Survey of mechanical properties of fabrics.
Basic equations: Hook's Law for extension and
shear, typical load-extension curves for various
fabrics, parameters, which determine the fibres
and fabrics bending rigidity.
Mechanical properties of fabrics assessed
manually when purchasing a cloth or garment in a
shop:
1.
Fabrics thickness and compressibility
(between 2 fingers, immedia-tely)
2.
Warm-cool feeling of fabric (within several
seconds, by fingers or when fabric lies on the
table)
3.
Friction force and perfile (when moving a
finger against fabric surface)
4. Bending rigidity (bending among 3 fingers)
5. Extensibility (pulling between both hands)
6. Shear rigidity (with both hands when fabric lies
on the table)
Relation for the deformation y (in the axis
perpendicular to the fabric plane) of an inclined
fibre protruding from a fabric under the angle α
between the fibre (of diameter 2r and length l) and
a fabric, when the fibre is bent by a force F
perpendicular to a fabric:
y
=
F
l3
cos2α
sinα
/
3
E
(3)
where the inertia momentum I [m4] of a fibre is
I = π d4 / 64
I
(4)
The equations indicate, that the fibre deformation
is proportional to the 3rd power of the fibre length
and indirectly proportional to the 4th power of its
diameter. That is why the micro-fibre fabrics, even
if the protruding fibres are short, deform easily
under pressure to certain extend and partially copy
the acting body. Thus, the contact area is always
large, the amount of heat taken away form the
contacting body is high and the contact feeling is
cool, in spite of the smooth and pleasantly soft
surface. Similar phenomenon appears after the
enzymatic or chemical treatment of fabrics: this
relatively drastic action results in the
disintegration of the fibre ending into several fine
micro-fibrils, which behave as micro-fibres.
Then, the enzymatic treated fabrics reveal also
cool feeling (high thermal absorptivity),
accompanied by smooth, pleasant feeling.
The bending rigidity B of such fabrics, however, is
sometimes too low, as follows from the
consideration placed at the end of this chapter.
On the other hand, any mechanical treating of
fabrics, like brushing or carding, brings the
warmer feeling, because the original compact and
smooth plane surface of dense woven fabrics with
high mass and hence high thermal capacity is
being replaced by the irregular surface featuring
lower mass, irregular thickness of a structure
composed of some soft and
easily deformed fibres, but some surface fibres
are not split, and due to their relatively big
diameter and short length they do not bend easily
under pressure, thus conserving the surface less
compressible, but full of thermal insulating air
pores of low thermal absorptivity.
3.3. Yarn and fabrics hardness (compressibility)
as a function of their packing coefficient μ
A new expression for yarn hardness or
compression modulus Ec [Mpa] according to
NECKAR (Prof. B. Neckar, Tech. Univ. of Liberec), k
means the proportionality parameter in Mpa,
depending on fibre material and processing,
μO means the lowest possible level of packing,
e.g. 0,8 for cotton yarns:
Ec=k3μ3[1+2(μ/μo)3]/[1-(μ/μo)3]4
(5)
Bending rigidity of fabrics is an important fabric
comfort parameter, since sometimes garments
require low bending rigidity (silhouette skirts,
pullovers, socks, all kinds of underwear), but good
appearance e.g. of men's suits, trousers etc. is
based on fabrics of higher and defined bending
rigidity B. In the classical mechanics of elastic
solids, the bending rigidity is given by a product of
the purely material parameter E [Pa] called initial
elastic modulus, and the inertia momentum I [m4],
given by the fabric structure and dimen-sions.
For the high density woven fabric of thickness
h and of width b the fabric bending rigidity, under
certain assumptions, the fabric bending rigidity
may be estimated by the following expression:
B = E . I , I = b.h3/12
(6)
3.4. Drape angle - a new method of drape
determination
One of the parameters, which characterises the
wearing comfort of clothes is fabric drape. Due to
easy way of its evaluation by means of the
Cuisick’s instrument an increased attention is
dedicated to this parameter, but the proper device
is quite large and requires relatively complicated
opto-electronic system. Also the proper measuring
procedure is time consuming. That is why we
cannot find this instrument or any similar
drapemeter in the factory labs, they are used in the
textile research units only.
3.4. Drape angle - a new method of drape
determination
One of the parameters, which characterises the
wearing comfort of clothes is fabric drape. Due to
easy way of its evaluation by means of the
Cuisick’s instrument an increased attention is
dedicated to this parameter, but the proper device
is quite large and requires relatively complicated
opto-electronic system. Also the proper measuring
procedure is time consuming. That is why we
cannot find this instrument or any similar
drapemeter in the factory labs, they are used in the
textile research units only.
Fig. 2 Measurement of Drape Angle
Fig. 2 Measurement of Drape Angle by means of a
special tool
(table) and moving this sample towards the sharp
(90O) corner of the table in such way, that the axis
of the 90o angle coincides with the warp or weft
direction. The fabric motion stops, when the peak
of the corner reaches the center of the sample.
Then the fabric folds and forms a direct edge,
whose inclination φ against the horizontal plane
we measure. The sin φ value measured by means
of simple ruler – see the Fig.2-then characterizes
the level of drape. The fact, that this parameter, in
some extend, does not depend on the length of the
inclined fabric edge indicates,
that this inclination is a certain fabric property,
which depends on composition, mass and
structure of the fabric. A certain evidence, that this
inclination may characterize the fabric drape
results from the fact, that materials like paper with
high shear stiffness do not fold in our test, they
just bend, and hence do not create the drape edge.
Theory of fabric drape
According to the Niwa and Seto regression
equation given below,
DA = DA=C0 + C1 (B/W)0,33 + C2 (G/W) 0,33
(6)
the drape coefficient should depend not only on
the fabric bending stiffness, shear stiffness and
fabric mass, but also on the levels of their bending
and shear hysteresis. Recently, the effect of fabric
mechanical properties on drape coefficient was
analyzed in 2003 by Militky and Hes.
Experimental determination of correlation between
Drape angle and Drape coefficient
To confirm the principal correlation between the
new Drape angle (DA) method and Drape
coefficient (DC) according to the Cuisick´s method,
90 woven fabrics made of cotton, linen, viscose
and their blends with nylon and polyester were
tested by the mentioned procedures. Square mass
of these samples varied from 50 g/m2 to 390 g/m2.
Every sample was measured 8 times. whereas the
axis of the table corner is perpendicular to the
fabric edge Separate measurments along the weft
and warp directions were made. The edge length in
first series of measurement reaches 5 cm, in the
second series it was 10 cm.
From the presented figures follows, that best
correlation of the new Drape Angle method with
the Cuisick classical method exhibit the C/E
sample orientation for the edge length 5 cm.
útek
y = 135,02x - 24,561
R2 = 0,6712
Regresní křivka
100,0
osnova
y = 125,67x - 19,875
R2 = 0,6793
Cuisick [%]
80,0
60,0
útek
40,0
osnova
20,0
0,0
0,00
0,20
0,40
0,60
0,80
1,00
metoda ohybem přes roh stolu [1]
Fig. 3 - Correlation between the DC and DA
methods
The correlation coefficient for the weft direction
was R = 0,717, and for the warp direction the R
reached 0,759. Unfortunately, we cannot directly
correlate any of this direction with the Cuisick
Drape coefficient, since the Drape coefficient
involves the whole fabric. Therefore, we have also
correlated the average value of DA for weft aned
warp directions with the DC data, with the resulting
level of correlation coefficient R = 0,767. Since this
result was verified for very large set of fabrics, the
practical verification of the new method can be
considered as verified. Nevertheless, other
unpublished results show, that this new simple
and cheap method may emphasize more the effect
of shear rigidity then the classical method,
which is a positive result, since the evaluation
of shear rigidity of fabrics by other methods is
quite complicated.
3.5.Methods of objective evaluation of sensorial
comfort of garments and fabrics
German method of objective evaluation of
complex sensorial comfort of worn garments
based on large experimental investigation. I is
called index, independently of its dimension. The
scales for TK (Wear Comfort, in German
Tragekomfort) extends from 1 to 6, where 1 is the
best level, 6 is the worst level).
Sensorial comfort
TK H   1 i mt   2 i k   3 i B   4 i o   5 nk   6 s   ( 7)
where particular parameters mean:
imt index of water vapour transmission
io surface index
nk number of contact points
ik index of lepivosti
iB index of wetting
s bending rigidity
Numerical values of constants:
1 = -2,537
5 = 1,71.10-3
2 = 1,88.10-2
6 = 3,86.10-2
3 = 2,29.10-3
 = 0,36
4 = 2,09.10-2
Determination of thermophysiological comfort
is similar:
TKT   1 i mt   2 Fi   3 K d   4  T   5 K f  
imt
Fi
Kd
T
Kf
index of water vapour transmission
dynamic vater vapour absorbtion [%]
liquid moisture buffering coefficient
temperature buffering coefficient [K.min-1]
moisture permeability
[g.m-2.hmbar-1]
Numerical values of constants:
1 = -5,640
4 = -4,512
2 = -0,375
5 = -4,532
3 = -1,587
 =11,553
(8)
Kf
moisture permeability
[g.m-2.hmbar-1]
Numerical values of constants:
1 = -5,640
4 = -4,512
2 = -0,375
5 = -4,532
3 = -1,587
 =11,553
Total comfort:
TKtot = 0,35 . TKH + 0,65 . TKT
3.6.Objective measurements of tactile mechanical
properties (FOM) of fabrics by means of Kawabata
(KES) instruments and their correlation to Handle
Values evaluation
4 measuring modulus, 16 parameters measured.

Fabric friction and perfil measurement

Fabric load/extension and shear force/shear
angle dependences

Fabric thickness and compressibility
measurement

Fabric beding rigididy dependence on
curvature determination
Comparison of Hand Values with FOM parameters.
Assesment of Total Hand Values. Kawabata-Niwa
regression equations for fabrics.
3.6.1.Determination of friction coefficient of textile
fabrics
Friction coefficient belongs to the important
parameters of textile fabrics, and its value affects
both their behavior during confectioning, and their
contact comfort parameter called handle. Feeling
of friction influences customer´s opinion when
buying new cloth for suits or skirts, and the
possibility of its precise objective evaluation even
in shops and markets would mean strong tool of
textile marketing.
Unfortunately, common instruments for the friction
assessment are too large, and their operation is
cumbersome.
The aim of research based on the above mentioned
torque measuring instrument was to design a
small portable instrument which is easy to operate.
New measuring method of the fabric friction
measurement
The principle of the instrument depends in manual
application of mechanical torque momentum by
means of hand rotation and the measurement of
the peak value of this momentum applied in the
specific friction torque measuring tool.
The measuring unit was designed in mechanical
version, electronic analogue version and also in
electronic digital version. All instrument versions
should exhibit the possibility of recording the peak
value of the applied torque momentum.
The mechanical version, equipped by the testing
needle (1) used also for the hardness
measurements in yarn packages, is displayed in
the Fig. 4. The principle of recording the peak
torque momentum depends in the use of torque
spring inside the instrument body (2).
1
2
3
4
Fig. 4a. The measuring unit equipped by a needle
for the measurement of the package hardness
The more is turned the instrument handle (3), the
higher is the torque momentum in the main shaft
of the instrument. The maximum angular
displacement,
and
hence
the
maximum
momentum, is then displayed by the extreme
position of the slippage dial (pointer).
The electronic versions of the instrument are
based on torque the ultra-thin wall tube, whose
small angular deformation is measured by means
of special strain gages, fixed on the tube wall
under the 45o slope. The strain gages are fully
temperature compensated. One end of the tube is
manually turned, the other end carries the proper
measuring tool.
The strain gages signal is conducted to the
Wheatstone bridge and the processed by means of
a digital micro-controller or PC together with an
A/D converter.
As shown in Fig 4b, surface of the ring shaped
body of diameters D and d, rubs against the flat
surface due to the force P. The torque momentum
M of this dry clutch and consequently the friction
coefficient  are given by the following equations :
D/2
M  2... .  p.r dr
3
d /2
3M D 2  d 2
. 
P D3  d 3
P
4P
p 
A  .( D 3  d 3 )
P
d
D
Fig. 4b Geometry of the friction ring used in the
tester
The force P causing the pressure p results from
the mass of the measuring ring (here, the mass
inertia affects partially the level of the momentum
M at the beginning of the measurement) or may be
assured by other, recently developed method,
which is not negatively influenced by the ring
mass.
3.7. FOM by means of the FAST instruments and
related snake diagrams
3.8. Non traditional methods of FOM
Pulling a fabric through a short hollow cylinder of
approx. 15 mm diameter and recording the pulling
force as a function of the fabric displacement
reflects the effect of several mechanical
properties, but the specific calibration is almost
impossible.
Also pulling a fabric strip by a moving straight
edge into a gap of certain width (Handle-O-Meter)
reveals a mixed effect of fabric bending rigidity,
compressibility and surface friction.
L. Hes and Yi Li (Hong Kong Polytechnic
University) designed and manufactured an
intelligent Hand Simulator, which should measure
in one step and on one sample all thermal and
mechanical
fabric
characteristic
commonly
detected by a customer when buying the cloth and
compare these characteristic with the subjective
ones.
3.9. Instruments For the Evaluation of Thermal
Contact Feeling of Textile Fabrics
Warm-cool feeling means the feeling we get when
the human skin touches shortly any object, in our
case textile or other fabric used in clothing,
furniture or carpets. It was found, that this
parameter characterises well the transient thermal
feeling which we get in the moment, when we put
on the undergarment, shirts, gloves or other textile
products. Since this feeling strongly affects the
choice of people when buying the clothes or garments, the objective assessment of this feeling
became very important in the last decade.
The first instrument, which was able to evaluate
the warm-cool feeling of fabrics objectively, was
developed by YONEDA and KAWABATA in 1983.
They have introduced the maximum level of the
contact heat flow qmax [W/m2K] as a measure of
this transient thermal characteristics, and
KAWABATA has published the first objectively
determined values describing the thermal-contact
properties of textile fabrics. Their instrument,
called THERMO-LABO, was commercialised. In
1986 an other instrument for the objective
evaluation of warm-cool feeling of fabrics, but of
different concept, was completed at the Technical
University in Liberec.
This
computer
controlled
semi-automatic
instrument called ALAMBETA calculates all the
statistic parameters of the measurement and
exhibits the instrument auto-diagnostics, which
avoids faulty instrument operation. The whole
measurement
procedure,
including
the
measurement of thermal con-ductivity , thermal
resistance R, qmax, sample thickness and the
results evaluation, lasts less than 3 -5 min. As the
objective measure of warm-cool feeling of fabrics,
so called thermal absorptivity b [Ws1/2/m2K] was
introduced. The meaning of this parameter
(formerly used in the civil engineering and
ergonomics) is explained in next paragraph.
Fig. 5
Heat flow between a skin and a fabric
Provided that the time of thermal contact between
human skin and a fabric is short, textile fabric was
idealised to a semi-infinite body of thermal
capacity c[J/m3] and initial temperature t2.
Transient temperature field between human skin
(characterised by a constant temperature t1) and a
fabric is then given by the following partial
differential equation
(t / ) = a ( 2t / x2)
(9)
and can be used for the calculation of the initial
level of heat flow q passing between the skin
(characterised by a constant temperature t1) and
textile fabric according to the next equation, whose
derivation for the boundary condition of 1st order
is similar to derivation of the Eq. (10):
qdyn = b ( t1 - t2 ) / (   )1/2
(10)
Thus derived thermal absorptivity b [Ws1/2/m2K] is
given by the relation:
b = (c)1/2
(11)
As it can be see, the level of thermal absorptivity
depends neither on the temperature gradient
between the fabric and skin, nor on the
measurement time. This value just depends on the
contact pressure, which also correspond to the
real situation. The pressure is adjustable.
The simplified scheme of the instrument is shown
on Fig. 6. The principle of first version of this
instrument depends in the application of ultra thin
heat flow sensor 4, which is attached to a metal
block 2 with constant temperature, which differs
from the sample temperature. When the
measurement starts, the measuring head 1
containing the mentioned heat flow sensor drops
down and touches the planar measured sample 5,
which is located on the instrument base 6 under
the measuring head. In this moment, the surface
temperature of the sample suddenly changes and
the instrument computer registers the heat flow
course. Simultaneously, a photoelectric sensor
measures the sample thickness.
All the data are then processed in the computer
according to an original programme, which
involves the mathematical model characterising
the transient temperature field in thin slab
subjected to different boundary conditions. To
simulate the real conditions of warm-cool feeling
evaluation, the instrument measuring head is
heated to 32ºC (see the heater 3 and the
thermometer 8), which correspond to the average
human skin temperature, while the fabric is kept at
the room temperature 22ºC. Similarly, the time
constant of the heat flow sensor, which measures
directly the heat flow between the automatically
moved measuring head and the fabrics, exhibit
similar value (0,07 sec), as the human skin. Thus,
the full signal response is achieved within 0,2 sec.
1
2
3
8
11
H
6
4
7
5
9
10
Fig. 6 Principle of the ALAMBETA instrument
The validity of thermal absorptivity as a new
warm-cool feeling parameter of fabrics was
confirmed by several tests where the results of
relative subjective feeling of 100 persons were
compared with the values of thermal absorptivity
found by means of the ALAMBETA instrument. It
was found, that practical values of thermal
absorptivity of dry fabrics range from 20 to 300, –
see Tab. 1. The higher is this value, the cooler
feeling represents.
Tab. 1
ALAMBETA
EFFECT OF FABRIC STRUCTURE, COMPOSITION AND
TREATMENT
ON
THE
LEVEL OF
THERMAL
ABSORPTIVITY b [Ws1/2/m2K], contact pressure 200
kPa
2040
Micro-fibre or fine PES fibre non-woven insulation
webs
3050
Low density raised PES knits, needled and thermally
bonded PES light webs
4090
Light knits from synthetic fibres (PAN) or textured
filaments, raised tufted carpets
70–
120
Light or rib cotton RS knits, raised wool/PES fabrics,
brushed micro-fibre weaves
100150
Light cotton or VS knits, rib cotton woven fabrics
130180
Light finished cotton knits, raised light wool
fabrics
150200
Plain wool or PES/wool fabrics with rough surface
180250
Permanent press treated cotton/VS rough weaves ,
dense micro-fibre knits
250350
Dry cotton shirt fabrics with resin treatment, heavy
smooth wool woven fabrics
300400
Dry VS, Lyocell, silk weaves, smooth dry resin-free
heavy cotton weaves (denims)
330500
Close to skin surface of wetted (0,5 ml of water)
cotton/PP (or spec. PES) knits
woven
450650
Heavy cotton weaves (denims) or wetted knits from
spec. PES fibres (COOLMAX)
600750
Rib knits from cotton or PES/cotton, knits from microfibres, if superficially wetted
750
Other woven and knitted fabrics in wet state
1600
Liquid water (evaporation effect not considered)
As results from the table, the thermal - contact
feeling of the fabrics is strongly affected by their
structure and composition. It was found, that fibres
and fibre polymers of higher moisture regain,
provide also cooler feeling. Therefore, the warmest
feelings can be achieved at fabrics made from
PVC, PP, PAN, whereas viscose, flax, cotton and
PAD fibers show the coolest feeling. Which feeling
is better, depends on customer: for hot summer
garments cooler (cotton) feeling is demanded,
whereas in the north of Europe warmer clothing,
based on the PES/wool is preferred.
An important aspect of the “warm-cool” feeling
evaluation is the change of this feeling when the
textile product gets wet. Because the time of the
warm-cool feeling evaluation of samples in the
ALAMBETA instrument is very short, less than 3
minutes, the evaluation of humid samples is
reliable (the sample does not turn dry during the
measurement). Because the thermal conductivity
and thermal capacity of water is much higher than
these of dry textile structure, the negative feeling
of coolness of garments moistened by sweat can
exceed 1000.
Since the thermal absorptivity is mainly the
superficial property, its level can be changed by
any superficial or finishing treatment, like raising,
brushing and coating. The instrument was
commercialised by the Czech SENSORA company.
3.10. Moisture absorbtivity of fabric
Many people believe, that 100% cotton underwear
(t-shirts) provide the best thermal contact
comfort, even in hot days, due to its easy and fast
sweat sorption (wetting), and their experience
based on common life of a clerk or a
bussinesman
confirms
this
statement.
Nevertheless, when the wearer has to exhibit
some physical effort, the excess of the sweat
keeps accumulated in the cotton fabric in the
proximity of sweating glands for long time and
causes thermal discomfort. On the other hand,
when we wear the PES/cotton fabrics in hot day,
the thermal discomfort, appears as well (even
without physical effort), but such fabric gets dry
soon.
Some customers believe, that both fabrics differ in
their water vapour permeability mainly.
In order to explain the effect of this parameter,
various underwear fabrics were measured in this
study. From the measurements made on the
PERMETEST (Sensora) instrument (see in Tab. 2)
resulted, that water-vapour permeability of the
measured underwear fabrics depends more on
their mass per area then on their composition, and
that in all cases the relative vapour permeability
was very good, exceeding 15%.
The next parameter in question is the moisture
sorption capacity (absorbency) of shirt fabrics.
There are some other methods to determine this
parameter. Nevertheless, the moisture absorbency
characterises just the specific moisture retention
corresponding to the state of full saturation of the
fabric volume by water or sweat, and is directly
proportional to the fabric mass. No transient
aspects are considered here, and no different
boundary conditions of moisture transmission
between the skin and a fabric are respected. A
survey of other techniques to measure transplanar
liquid transport into fabrics published Kissa in
1995.
Nevertheless, all the found measuring methods are
not suitable for simple standard measurements of
transient fabric wetting, due to quite complicate
preparation of the measurements and poor
dynamic properties of some of these methods.
Moreover, the reduced comfort caused by wearing
e.g. the PES/cotton shirts in hot day is felt mainly
in the moment, when the suddenly wetted fabric
touches the skin. Consequently, local cool feeling
occurs, which is considered unpleasant. Within the
con-tact time, heat is transferred by conduction
through a thin intermediate layer, created by wet
outstanding fibres. Thus, the boundary condition
approximates to the heat transfer of 1st order,
which should be respected within a measuring
method in question.
Therefore, the first objective of the research work
was to develop a method of an indirect
experimental determination of the so called
surface moisture absorptivity B, whose higher
level apparently increases the contact comfort of
wet fabrics and on the contrary. Such parameter
should present an integral factor, embracing the
effect of moisture surface adhesion (given by the
contact angle ) and the moisture conduction
(depending on capillary forces). The highest
surface moisture absorptivity appears in the
moment, when the adhesion and conduction
mechanisms, which in some cases act again each
other, create a specific synergic effect.
Introduction of Moisture Absorptivity
The amount of liquid inside any porous structure
or textile fabric can be expressed in terms of the
fabric free volume saturation s. Thus, for s = 0 the
fabric is dry, and for s = 1 all the pores are full of a
liquid. In this case, the saturation propagation
within a fabric, either along its surface, but also
perpendicularly
to
its
surface,
can
be
characterised by the classical partial differential
equation of diffusion processes:
(s / ) = A ( 2s / x2)
(12)
where A [m2/sec] is so called moisture diffusivity.
This parameter is for textile fabrics sometimes
moisture dependent due to swelling. The solution
of equation of this kind for A = const is generally
known. If we consider just short time moisture
conduction, then we can convert a textile fabric to
a semiinfinite body, where the 1st order boundary
condition is applied. In this case, the moisture
saturation propagation in the x direction is given
by the equation
s = erfc (x /2 A1/21/2)
(13)
The experimental determination of the moisture
diffusivity from the moisture propagation along the
measured fabric is possible. Unfortunately, the
moisture diffusivity in this form does not
characterise the volumetric capacity V of the fabric
expressed in this case in m3/m2s to conduct the
moisture (sweat) from the contacted skin away
towards a fabric interior. To cope with this task, a
Darcy law modified for the saturation gradient
should be introduced as follows:
V = - s (s/x)
(14)
where s [m2/s] is the volumetric moisture flow
conductivity, which is proportional to the fabric
permeability. In the next step, we should remind,
that in the first Fick´s diffusion law, which is used
to express the mass flow in the form formally
identical with Eq. (14), the same diffusion
coefficient D occurs, as in the second Fick´s law
for transient mass transfer by diffusion. By
simplifying the problem solved to a simple
diffusion, we can express the moisture flow
conductivity in Eq. (14) s by means of the
moisture diffusivity A. From applying this relation
in equation (13) follows:
V = A1/2(s/1/21/2)
(15)
The first term in this equation fully
characterises the fabric ability to absorb the
moisture from any moist surface which contacts
the fabric. Then this so called moisture
absorptivity B [m3 s1/2] is defined by the next
relation:
B = A1/2
(16)
Many researchers have already measured the timedependent longitudinal wicking of fabrics. From
these results, the moisture diffusivity A could be
determined and its square root used for the
calculation of the spontaneous moisture uptake
according to Eq. 15. Nevertheless, this approach
may produce inaccurate results, since longitudinal
wicking rates not always correlate with the
corresponding transplanar ones, due to the
complexity of the wicking processes, which
besides the diffusion processes include capillary
penetration of moisture inside fabrics, and also
moisture absorption of the fibre surface.
Indirect Method of the Moisture Absorptivity
Measurement
The suggested method is based on the objective
evaluation of warm-cool feeling perceived by a
wearer of a cloth, which suddenly comes into
contact with a wetted skin. In this moment, the
cotton fabric absorbs the liquid sweat rapidly, and
conducts it away from the fabric surface towards
to the fabric inerroir. Due to high adhesion forces,
the sweat keeps accumulated in the fabric close
the places where the sweat was generated. If the
amount of sweat is not too high, within a short
time the moisture concentration close to the fabric
contact surface reduces, and the wearer feels the
pleasant contact of nearly dry fabric.
The other mechanism of achieving the pleasant dry
feeling of underwear and shirts is based on the use
of PES microfibres, which, due to higher surface,
absorb in some extend the humidity also, but the
liquid sweat is rapidly distributed by capillary
forces in larger area surrounding the perspiration
zone, thus reducing the average relative humidity
of fabric under the limit, which would result in
unpleasant wet feeling.
Unfortunately, this
mechanism requires also some additional
dymamic contact forces typical for sport activities.
In the case of blended fabrics containing too much
poorly absorbing PES fibres of common section
and fineness, the sweat keeps adhered on the skin,
and provokes an unpleasant cool feeling due to
sweat evaporation.
The suggested method is based on the objective
evaluation of cool feeling effect within an
experimental procedure, which simulates the real
fabric wearing conditions described above.
Methodology of the Indirect Measurement of the
Fabric Moisture Absorptivity
The intention of this research was to characterise
the contact comfort felt by a wearer of a shirt
during a hot day. For this purpose, a special thin
interface fabric was found, which should simulate
the effect of a sudden sweat discharge on the skin.
This sweat simulator should be thin, in order not to
influence (in dry state) the thermal capacity of the
measured fabric, but this interface fabric should
absorb a certain amount of liquid injected in the
centre of this interface fabric and it should
distribute the liquid fast and uniformly within a
circle of approx. 50 mm diameter. After some trials,
a thin PES Coolmax knit was found to fulfil all
demands.
At the beginning of the measurement, the
ALAMBETA instrument is switched on and the
measured underwear is placed on the measuring
base of the instrument. Then, the volume of 0,2 ml
of water (containing detergent) was injected on the
centre of the interface fabric surface, covered by
the viscose fibres. Within one minute, the liquid
distributed uniformly within a circle of 45-50 mm,
and stopped. When this occurred, this interface
fabric was inserted into the space between the
measured sample and the centre of the measuring
head of the instrument - see Fig. 7. At the same
time, the interface fabric and the measuring head
of the instrument dropped down towards to the
measured underwear or shirt fabric.
Within a few seconds, the liquid from the interface
fabric was more (in case of pure cotton shirt) or
less (in other cases) taken away by absorption into
the lower fabric. If this fabric exhibits low
absorption, the thermal capacity of the interface
fabric is maintained quite large and the initial level
of thermal absorptivity b is significantly higher.
In the case of measurement of “warm-cool” feeling
on pure cotton fabrics, characterised by higher
moisture absorptivity, the moisture is rapidly
distributed within the whole thickness of the fabric,
so that the interface fabric gets nearly dry, and the
instrument shows a lower level of the resulting
thermal absorptivity.
Guiding shaft
Measuring
head
Upper heat
flow sensor
Interface
fabric
Bottom sens.
sensor
Fabric
fated
Fabric
Fig. 7 - Simulation of the underwear wetting and
wicking by means of the ALAMBETA instrument
Theoretical Analysis of the Underwear Wicking and
Wetting Effect on Cool Feeling
In the new version of the ALAMBETA, not only one,
but two heat flow sensors are applied, as shown
on Fig. 7- see the second sensor. This enables to
simplify the heat flow signals evaluation and
moreover, the instrument can check the level of
heat, which is during the measurement conducted
away (in the surrounding air) from the sample. This
increases the measurement precision.
During the measurement, the computer integrates
the heat Q[W] passing through both heat flow
sensors, which is accumulated inside the
measured sample, according to the Eq. 17:
Q = q() d =
T

q1 –qo)( d
0
(17)
The measurement finishes for the time level T,
when q1 (T) equals qo (T). Then, the heat Q causes
the increase of the average temperature inside the
measured sample, as follows:
1
Q = moco (t1 – to)
2
(18)
This equation then yields the surface related heat
capacity moco [J/ m2]. Simultaneously, the sample
thickness h[mm] is measured and used for the
determination of the fabric heat capacity oco
[J/m3] from the equation
oco = moco/h
(19)
The consequent steady state measurement of heat
flow passing through the sample then enables the
easy determination of the coefficient of thermal
conductivity [W/m.K] and the fabric thermal
resistance R[m2K/W]. The warm-cool feeling
parameter - thermal absorptivity, then follows from
Eq. 11.
In the next step, the mentioned measuring
principle will be applied in the simple analysis of
the wetting and wicking simulation. In this case,
heat balance of the space between both heat flow
sensors should include the effect of heat capacity
per area m1c1 of the interface fabric and ist initial
moisture Mwcw, provided that the measuring head
has just dropped down and completed the thermal
contact between the interface and underwear
fabrics:
1
QM = (moco + m1c1 + Mwcw)(t1 – to)
2
(20)
Within a few seconds, the moisture will be
absorbed by the underwear and distributed in its
volume. In fabrics exhibiting good moisture
conduction the sweat will be transported by the
capillary action outside the area of heat flow
sensors. Hence, the effective moisture content in
central part of the underwear will be reduced to
lower level mw, thus reducing the volumetric
thermal capacity of the system consisting of
interface fabric and underwear. The integral heat
detected by both heat flow sensor will be as
follows:
1
Qm = (moco + m1c1 + mwcw)(t1 – to)
2
(21)
Because mw  Mw, and due to the fact, that the
specific heat of water cw is very high – approx. 3
times higher than that of fabrics, even small
differences in the moisture amount absorbed form
the sweat simulating fabric and conducted away
form the sensing area of heat flow sensors will
result in relative big changes in heat capacity of
various tested fabric system and hence in big
changes in their thermal absorptivity levels. In fact,
the resulting sensitivity will be even bigger, due to
varying evaporation effects, which were not
considered in this simple analysis (the more
moisture keeps in the interface fabric after contact,
the cooler is ist surface, and the higher is the
resulting thermal absorptivity).
Experimental Results
The composition of the investigated plane fabrics
varied from 100% cotton to 100% PES or PP fibres.
Medium values of the results are shown in the
following Table 2.
Tab. 2. Cool feeling (thermal absorptivity) of
various fabrics measured by the ALAMBETA
instrument when simulating their sudden thermal
contact with wetted skin, pressure 200 Pa
Thickness
H[mm
]
CV up
3%
45% cotton, 45% PP +PAD
Italian 2 layers smart knit
1.15
Thermal
conducti
vity 
[mW/mK
]
CV up
3%
105
50% cotton 50% PP spec.
struct. Czech smart knit
0,66
100
43,0
421
100% spec. Section PP +
common PP, Czech 1
layer smart knit
1,21
112
40,2
430
SAMPLE COMPOSITION
AND STRUCTURE
Relative
water vapour
permeability %
CV up
6%
41,4
Thermal
absorptivity b
[Ws1/2/
m2K]
CV up
5%
415
100% spec. Section PES,
single layer knit Dupont
Coolmax
0,54
97.2
32,1
443
100% cotton denim
0,71
86,2
13,5
452
100% cotton shirt, no resin
0.43
83.1
22,5
508
100% cotton shirt, no resin
0.38
90.1
24,7
565
70% cot.+ PES woven shirt
0.21
78,7
25,4
731
35% cot.+ PES woven shirt
0,28
120
24,8
751
75% cot.+ PES woven
shirt
0,23
88,9
19,4
875
35% cot.+ PES woven
shirt
0,26
123
22,4
935
100% cotton shirt resin
treated
0.22
149
22,8
1178
Results Evaluation

With an increasing portion of PES fibres in
common woven shirt fabrics increases the
unpleasant cool feeling (i. e. increases thermal
absorptivity) when worn in conditions of surface
wetting, which matches the practical experience of
wearing the tested shirts.

Special smart fabrics with improved thermal
comfort properties like double layered knits or T
shirts knitted from Coolmax or Coolplus (Taiwan)
modified PES fibres reveal more pleasant contact
feeling in conditions of superficial wetting.

Exceptionally some cotton/PES blend fabrics
made from common fibres may exhibit relatively
good thermal contact comfort in the wet state,
even with quite high portion of PES fibres, due to
some unknown effect or due to a special fabric
structure (confirmed by wearers).

Cotton shirt weaves containing too much
chemical agents deposited inside the fabric may
show worse contact comfort feeling in the wet
state, in spite of the fact, that their steady-state
water vapour permeability keeps very high.
4.Thermophysiological clothing comfort - principles
Fig. 8 Thermoregulation system of human body
4.1.Environmental parameters of human life: air
relative humidity φ, air velocity vA, dry
thermometer (or air) temperature tA, wet bulb
(thermo-meter)
temperature
tWB
(strongly
dependent on φand vA, and globe temperature tG,
which is measured in centre of big black globe,
thus expressing the effect of solar radiation. The
integral environmental effect expressed in terms of
the wet bulb globe temperature tWBG :
tWBG = 0,7 tWB + 0,2 tG + 0,1 tA
(21)
Examples of groups of environmental parameters,
which offer the thermo-physiological comfort
under various physical activities, provided that the
level of the radiation temperature (emitted e.g. by
warmer walls) does not exceed the dry air
(environmental) temperature tA for more then 2OC:
Administrative work
tA = 21OC±3OC, φ = 55% ±15%,vA = 0,1 m/s
Light manual work, standing
tA = 19OC±3OC,φ = 55% ±15%, vA = 0,2 m/s
Heavy manual work
tA = 18OC±3OC,φ = 50% ±15%, vA = 0,4 m/s
Very heavy work
tA = 7OC±3OC, φ = 50% ±15%, vA = 0,5 m/s
4.2.Fundaments of human thermal physiology
Human body as a thermal engine with the
efficiency  = (5-25%).
Fig. 9 Human body as a thermal machine
Muscles transforming chemical energy into
labour L [J] (up to 50x increase from the resting
level). Energy carriers: carbohydrates (18 kJ/g),
fats (40 kJ/g) and proteins (19 kJ/g). Food
processing: stomach

absorption in small intestines

transport by blood

transformation into energy in cells or storing
as glycogen (C6H10O5) or fat.
Muscles work: energy input converts
adenosine diphosphate -ADP into adenosine
triphosphate (ATP). Most easily used energy
carrier: glucose . Aerobic metabolism (most
effective): C6H12O6 + 6O2 = 6 CO2 + 6 H2O + energy
(690 kcal/mole). Anaerobic metabolism: lactic
acids released. Energy storage: fat, 16-22% of the
body weight in a man, 22-34% in a woman (15-20%
in sportsmen). Much less stored energy in
glycogen and glucose. Protein amino acids used
for energy just in vital conditions (death of cells
involved).
Basal metabolism: approx. 1,1 W /kg of body
weight, minimum metabolic power Mmin reaching
50-100 W., heart rate 60-80 /min. Resting
metabolism: 1, 25 W /kg of body weight,
corresponding to the oxygen consumption 0,0035
L /min/kg of body weight (which is called 1 MET).
Heavy work requirements: even more then 10 W
/kg of body weight, heart rate exceeding 120 /min,
muscles consuming up to 70% oxygen available,
brain always 5%, internal organs suffering. Heart
pumping rate: from 25 litre/min to 40 litre/min for
sportsmen.
Temperature set points in hypothalamus: 37OC
for core, 33OC for skin.
Temperature limits: over 45OC:coagulation of
proteins, 0OC:breaking cell aparts due to ice
crystals. Deviation of core temperature 37OC ±2
OC affects body functions, deviations ±6OC are
lethal.
Sudomotor nervous pathways control the sweat
glands activities only, the vasomotor system
brings about the vascular dilation, constriction or
shunting, thus affecting the heat distribution
throughout the body.
Sweating level mp [kg/min, up to 10 kg/day] as the
function of real skin (tS > 32O C) temperature and
core (nuclei) temperature (tN > 37OC) due to
increased environmental temperature tE
mp = F1 (tS - 32 ) + F2 (tN - 37)
(22)
4.2.1.Definition of thermal comfort for lying or
resting human body:
thermal equilibrium, no muscular shivering nor
vasodilatation, no principal sweating (relatively dry
skin), skin temperature between 32 and 34OC, no
heat storage or loses. Changes of stored
(accumulated) heat:
ΔQAC=cspec.(0.35ΔtS+0.65tN),cspec=3300J/kg.K (23)
4.3.Equation of steady - state thermal equilibrium
of human body expressed in heat/time [J/sec]
units, it means in power Q[W] units.
(M
η- L)/A
+
L/
min
Du = (M - L)/ ADu
(M-L)/A
±q
±q
±q
Du
cond
conv
rad
(25)
(24)
- qres,c - qres,e - qins -persp = 0
Meaning of new symbols:
ADu is the surface of the average human
body, 1,8m2.
qconv heat flow [W/m2] by convection from the
skin surface
qconv = α Fcl (t*sk – ta) ADu
(26)
α = 2,38 (t*sk – ta)0,25
for natural convection
α = 3,5 + 5,2 var
for forced convection at var 0-1 m/s
α = 8,7var0,6
for forced convection at var over 1 m/s
qcond given by Eq. 28, at walking just 5 -10 w.
qrad given by Eq. 35
qres,c cooling by respiratory convection
qres,c = cp Va (tex – ta) ADu, which can be expressed
through metabolic power M as
qres,c = 0,0014 M (tex – ta)
qres,e cooling by evaporation at respiration
qres,e = L Va (Wex – Wa) ADu, which can
be expressed through metabolic power M as
qres,e = 0,0173 M ( pex – pa)
qins
cooling by insensible and permanent
evaporation from skin pores, approx.0,15 W/1 kg of
body mass
qpersp intensive cooling by means of principal
sweating glands controlled by brain hypothalamus
(sudomotor pathways) through adrenalin level, and
by means of smaller glands in
palms and soles
qpersp = w (pwv,sat – pwv,out)/Revap,tot
w means here skin wettedness, given by
fraction of the wetted skin skin surface related to
total skin surface
The heat and moisture transfer mechanisms
applied in the human body thermal balance are
explained in the next text in more detail.
4.4.Fundaments of heat transfer between human
body and environment by conduction, convection and radiation
4.4.1.Principal relations describing the heat
conduction:
Fourier's law, expressing the proportionality
among heat flow q [W/m2K], thermal conductivity
λ[W/m.K] and temperature gradient Δt/Δx:
q = - λ.Δt/Δx
(27)
Relation for thermal resistance R [m2K/W] of
fabrics, thin air layers and other plane materials of
thickness h [m]:
R = h /λ
(28)
Thermal resistance of air layer in clothing:
maximum for h = 5mm.
Total thermal resistance of clothing
consisting of full area individual layers:
RCL = R1 + R2 + R3 + . . .
RCL
(29)
skin surf.
underw.
med. fabric
outer fabric
transfer of heat,
moisture and air
body core
moisture
air
environment
I
II
III
air layers
laylaylayers vzduchu
Fig. 10
layers
Heat flow through clothing
Total heat flow - heat power Q*[W] through a
clothing of area ACL by conduction within the
temperature gradient Δt = tS - tE is then given by
the equation
Q= ACL . q = Δt . ACL / RTOT, where
(30)
R
TOT
= RCL + RE
4.4.2.Principal relations describing the heat
convection:
Heat is transferred by particles of fluids moving
with the velocity v [m/s]. The thermal boundary
layer thickness δis thick for the laminar fluid flow
and becomes thinner for the turbulent flow,
when the Reynolds dimensionless number Re
exceeds 2300 for any object of characteristic
dimension d [m].
Re = vd/ν, where ν[m2/s] means the dynamic
viscosity of the fluid.
The heat transfer coefficient αC [W/m2K] is
relatively low for natural convection, and increases
for forced convection. For the conditions typical
for the use of clothing, the heat transfer coefficient
can be also given by a simplified equation for all
air velocities
αC = 8,3 √v
(30)
The Newton's law for the heat flow transferred by
any kind of convection or conduction is as follows:
q =αC (t1 - t2) or q = (t1 - t2) /Rcl
(31)
where
Rcl
means thermal resistance of
garment or clothing.
Convection thermal boundary layer
important external thermal resistance
Rbl = 1/αC
presents
(32)
which should be included into the total thermal
resistance RTOT.
Sometimes we should also consider the heat loses
by radiation, given by the linear radiation heat
transfer coefficient αrad.
4.4.3.Principals of heat transfer by radiation
Generally, the heat flow passing through clothing
layers by IR radiation may reach up to 10 - 15% of
the total heat flow. In hot days or countries, solar
radiation, both visible and invisible, causes
principal thermophysiological discomfort.
Radiation UV, μm Infrared waves
Ultrashort Short
γ, X
0,19-0,38 0,75 - 1000μm
1mm - 1 dm 0,1-2m
Visible light 0,35 - 075 μm
Radiofequences
2 - 1500 m
Log wavelength λ →
Fig. 11 Spectrum of electromagnetic radiation
Radiation heat is transferred by visible (light) and
invisible electromagnetic waves.The visible part of
the electromagnetic spectrum involves the
wavelength Λ= 0.4-0,75 micrometer (μ),where sun
emits approx. 50% of its thermal energy. White
garments reflects a good part of this thermal
energy. The resting 50% is radiated in the invisible
infrared (IR) part of the spectrum (0,75 - 100 μ),
mainly in the near infrared part of the spectrum (till
2 μ). Here, the degree of reflection ρ<1 already
cannot be characterised by a white colour - we
cannot distinguish here any colours, but any
smooth surface reflexes IR radiation better can a
harsh, coarse surface. The-refore, the protecti-ve
clothing against heat should be white (or of
polished metal), and smooth.
According to the Wien's law, the lower is the
absolute temperature T[K] of the heater, the
shorter is the wave-length ΛMAX [ μ] corresponding
to the maximum level of the emitted energy, as
follows:
ΛMAX . T = 2890
(33)
Thus, heat flow transferred by radiation between
the sun and humans reaches its maximal level for
the green light (0,55 μm),whereas clothed humans
lose energy towards the common environment at
the wavelength approx. 10 μm. Some special fibres
contain ceramic particles,
which absorb the visible radiation with the degree
of emissivity (or absorbance) ε≈1, whereas for the
IR radiation this dimension less parameter is
substantially lower then 1.
When calculating the heat flow q [W/m2]
transferred by IR radiation between two clothing
layers (garments), we can use the relation for
parallel planes with the emissivity levels ε1,ε2 and
kept at temperatures T1 and T2 in IR permeable
environment as follows (σ= 5,67 x 10-8 is the
radiation constant):
q = σ(T14 - T24 ) / [ (1/ε1)+ (1/ε2) - 1]
(34)
In order to reduce the heat transferred through
clothing by radiation (e.g. in sleeping bags), the
textile layers can be coated by the vacuum
deposited aluminium.
Radiation heat flow transferred between a (clothed)
human of surface absolute temperature TS and a
homogeneous, cooler environment of the average
absolute temperature TE is given by en expression
q = σεS (T14 - T24 ) 4σεS [(T1+ T2)/2] 3 (t1- t2)
(35)
From the analogy with the convection heat
transfer, the linear radiation heat transfer
coefficient receives the form
αrad = 4σεS [(T1+ T2)/2] 3
(36)
High thermal resistance of nonwoven fabrics is a
frequent reason of their applications in protective
clothing, sleeping bags and related technical
textiles. New standards and higher requirements
result in the necessity of determination of thermal
resistance of these insulation layers with higher
precision. Therefore, several new measuring
instruments and methods appeared recently to
serve for these purposes. Majority of them is
based on the evaluation of steady
or unsteady heat flow passing between two plates,
which embrace the measured fabric.
Should the thin or low density fabrics be
measured, the portion of the heat transferred
between the plates by infrared radiation may reach
10-30% of the total heat flow. Convection is
generally negligible. In this case, the radiation
properties of the plates should affect the effective
thermal resistance of the nonwoven insulation
layer. The first objective of the next study is to
determine the portion oh heat, which, in common
textile fabrics, is transferred by infrared radiation.
The main objective of the paper is, however, the
experimental determination of the effect of the
surface emissivity of the measuring plates of the
thermal insulation measuring instrument, on the
measured thermal conductivity and thermal
resistance of selected relatively thin nonwoven
fabrics made of different materials.
The experimental procedure is based on a new
computer-controlled measuring instrument, which
measures the steady and transient thermal
characteristics of non-metallic materials within one
step. A brief description of this instrument is given
in the next chapter, along with the brief theoretical
analysis of the problem.
Thermal conductivity of textile fabrics
Thermal-insulation properties belong to the basic
properties of textiles fabrics and so they have been
studied and measured very thoroughly. Similarly,
the theoretical analysis of heat transfer through
fabrics was carried out by several investigators and
the most recent papers were published by
FARNWORTH, CAPS and UMBACH, HES and
STANEK. It was found that the mechanisms of
transfer of heat through textile fabrics depend
mainly on thermal conduction and radiation. This
was confirmed during an extensive experimental
investigation of heat transfer through woven and
nonwoven fabrics, which was conducted at the
Technical University of Liberec,
where the Grasshoff number Gr, describing the
effect of free convection, was always lower than
1000.
Based on new theory and a new high precision
measuring instrument, HES and STANEK derived
the following formula for thermal conductivity  of
textile fabrics with low density:
λ = A 1-
μ1  ν  +
μ(1  ν)
1  μ(1  ν) (1 
λA
)
λ PES
}  μ.ν.λ PES 
4h.σh3
0.188h(ν  1)μ
exp
2
r π
1
ε
(37)
Here, the first term on the right hand side
expresses the transmission of heat by conduction
in air gaps (proportional to thermal conductivity λA
of air) and through the polyester fibres (with a
thermal conductivity λPES 15 times higher than that
of air) oriented parallel with the surface. The
second term shows the heat conduction through
the fibres oriented perpendicular to the fabric
surface. The term μ represents the filling
coefficient of the fabric, and ν is the (idealized)
portion of fibres oriented vertically to the
isotherms in the fabric.
For the purpose of this paper, the more
important factor is the last right hand side term,
expressing the heat conducted by radiation, where
the classical dependence of heat flow on the 4th
power of temperature can be approximated by a
linear one:
rad =
4hT 3
0.188h(υ  1)μ
exp(
)
2
r
π
1
ε
(38)
Here, h is the thickness of the fabric, σ is the
radiation constant, T the average temperature in in the fabrics and ε and r the
emissivity and radius of
fibres.
As shown later, the portion of heat flow transferred
by radiation does not exceed 20% of the total heat
flow. Thus the linearity of the mathematic model is
conserved and the following relation can be used:
 = cond + rad
(39)
Nevertheless, in spite of the fairly low effect of rad
on total , the investigation of factors influencing
rad is important, because the technological ways
to reduce cond only (in order to increase the
insulation power of fabric) have already been
exhausted. As a result, many researchers are now
trying to reduce therad of textiles. Because of the
low contribution ofrad to the total level of λ, the
investigation of this factor creates strict demands
on the sensitivity and precision of the experimental
technique.
The instruments generally used for the
measurement of thermal conductivity  and
thermal resistance R of thin layers are not
sufficiently precise, because the changes in heat
flow caused by the low thermal resistance of
fabrics are nearly undetectable for classical
instruments of the BOCK (large skin model) type. A
recently developed instrument ALAMBETA, does
not exhibit this problem. Besides that, the new
instrument enables also the measurement of
transient thermal characteristics of textile fabrics,
where one of these characteristics can be used for
objective evaluation of warm or cool feeling. This
is important during short contact with the fabric, or
when wearing some fabrics (like trousers) which
come into intermittent thermal contact with our
skin.
Theoretical background of the experimental
procedure
To investigate the portion p of radiation heat flow
transferred through textile fabric, the next
procedure can be applied:
The method is based on the fact, that rad
increases with the mean temperature T in the layer.
Therefore, for two different mean temperatures T
(supposing T1=300 K and T2=315 K, which can be
adjusted at the instrument) and after applying Eq.
(3) we get:
for T =T1
cond + rad(T1) = 1
(40)
for T=T2
cond +  air +
(41)
rad
(T1)
. (T2 /T1)
3
= 2
Subtracting both equations, we obtain
rad = ( 2 -
1 +
air
/ [(T2 /T1)
3
- 1]
(42)
The effect of increased mean temperature on
thermal conductivity of the air trapped in fabrics
was considered by increasing cond in Eq.9 by
air = 0.00055 W/m.K,
(43)
which also reflects the relative portion of air in
the fabric (about 70%).
4.5.Fundaments of water vapour transfer between
human body and environment
Moisture (mass) can be transferred either by
conduction or by convection. The transfer force of
water vapour in clothing systems is the gradient
between the saturated vapour conentration or
saturated (maximal) partial pressure pWSAT [Pa] at
the human skin the actual environmental water
vapour concentration or its partial pressure pWE
[Pa]. The inverse ratio of these parameters
multiplied by 100 we call relative humidity φ[%]. In
countries, where the φis lower than 60 - 70 %,
humans can reach the conditions of reasonable
thermo-physiological comfort (due to the efficient
sweating) even under high air temperatures (in
deserts).
When the air relative humidity φexceeds 8085%, than no state of comfort is attainable at air
temperatures over 35OC.
Moisture (mass) transfer by conduction
The amount of transferred vapour (mass) m*
[kg/m2. s] is proportional to the
diffusion coefficient Dp [kg/m.s.Pa] and to the
partial pressure gradient
Δpparc /Δx
(44)
According to the Fick's law:
m* = - Dp .Δpparc /Δx = - Dp . (pWSAT - pWE)
(45)
Instead of the water vapour pressure gradient, also
the mass concentration gradient C [kg H2O/ 1kg
humid air] can be used in the above mentioned
expression:
m* = - DC. ΔC /Δx = - DC . (CWSAT - CWE)
(46)
The correlation between both forms of the
diffusion coefficient is then given by the state
equation of gases, comprising the molar density of
water vapour MW, universal gas constant R and
absolute vapour temperature T:
Dp = DC. MW /RT
(47)
Vapour is transferred by conduction (diffusion)
through fabrics and
gaps in garments or
in clothing systems. If there are no pumping
effects of free convection in clothing systems, the
water vapour resistance RW of gaps, given by the
equation
RWP = h / DP or RWC = h / DC
(48)
Can reach relatively high values. In textile fabrics
consisting of pores (channels), which present big
barriers for the moisture transfer, due to the fabric
surface porosity ε< 1 and increased channels
length (given by the tortuosity factor ξ>1), the
water vapour resistance RWF of fabrics can be very
high, according to the next expression:
RWP =ξ.h /ε.Dp
(49)
Therefore, due to the larger porosity, open
fabrics like knitted ones naturally offer much
higher water vapour permeability or lower water
vapour resistance then the woven fabrics
Moisture (mass) transfer by convection
The relation for the mass transferred by
convection is similar to the Newton Law:
m* = βp (pWSAT - pWE) =βC (CWSAT - CWE),
βp = βC MW /RT
(50)
Similarly, as the convection heat transfer
coefficient αincreases with the air velocity, the
convection mass transfer coefficient βp [kg/m2s Pa]
is also proportional to the air velocity.
Due to analogy between the heat and mass
transfer, the convection mass transfer coefficient
βC for low air velocities can be calculated by
means of the Lewis Law:
α = βC . cpA
(51)
Here, cpA [J/kg.K] is the specific heat of the humid
air.
4.6. Fundaments of wetting and wicking of
textile fabrics. Contact angle, adhesion.
4.7.Simple thermal model of a clothed human
body
Relation for the clothing/garment total thermal
insulation Rcl [m2K/W] in cold conditions, when no
principal
transpiration
is
involved,
and
homogeneous, full body covering textile layer is
considered:
q =[0,75(M-L)]/Acl=(33-text)/[(Rcl.v)+1/(αconv+ αrad)]
(52)
Here, the effect of ventilation and body movement
on thermal loses of a body is respected by means
of the ventilation coefficient v = F(air velocity,
fabric air permeability), v < 1. Factor 0,75 in the
first term reflects the heat loses by insensible
evaporation, respiration and cocuction.
5.Thermophysiological
evaluation
clothing
comfort
-
5.1.Measurement of thermal resistance and of
warm-cool feeling of fabrics, both in dry and wet
state, by means of the ALAMBETA computercontrolled device - see in Chapter 3.9.
TEMPERATUR
E SENSOR
RELATIVE
HUMIDITY
SENSOR
FAN
WIND CHANNEL
SAMPLE
POROUS LAYER WITH
HEAT POWER MEASURING
SYSTEM
MEASURING
HEAD
METALLIC
BODY
THERMAL
INSULATION
TEMPERATURE
SENSOR
HEATING
ELEMENT
WATER
INLET
Fig.12 Measuring facility
5.2.Evaluation of warm-cool feeling in simulated
conditions of medium and intensive sweating - see
in Chapter 3.10.
5.3. Measurement of water vapour resistance (in
dry and wet state) and heat of absorption of
fabrics, by means of the fast PERMETEST
instrument
Water vapour permeability of fabrics presents,
along with fabric thermal resistance, the most
important characteristic of clothing comfort.
That is why increased attention is paid to this
parameter in recent decades. Testing of this
parameter in official laboratories and the used
instruments are generally costly, time consuming
and requires of ten special samples cut from
pieces of fabrics. If these are large, their price
can increase substan-tially the total price of each
measurement. Moreover, the necessity of specially
sized samples avoids the non-destructive
measurements on tailored garments due to high
price of the completed products. That is why a new
friendly testing method and corresponding
measuring device PERMETEST that presents a
small „skin model“ were developed in the nineties.
The istrument was comerci-ased by the Czech
SENSO-RA Company, and under standard
laboratory condi-tions (at 22 °C and relative
humidity 55%–60%) it offers reasonable precisi-on
of measurement. Re-sults of measurement are
expressed in units defined in the ISO Standard
11092. The main advantage of this instru-ment is
the fast and non-destructive testing of wa-tervapour and thermal resistance / permeability of
textile fabrics.
Principle of the PERMETEST instrument
Slightly curved porous surface is moistened
(either continuously or on demand) and exposed in
a wind channel to parallel air flow of adjustable
velocity (Fig.12). A tested sample is located in a
small distance from the wetted area of diameter
about 80 mm and characterized by high thermal
conductivity. The amount of evaporation heat of
liquid water taken away from the active porous
surface is measured by a special integrated
system. Thus, very low time constant of the whole
system was achieved, resulting in short
measurement time – full signal is registered within
several minutes.
Besides basic elements described below (see also
Fig.12) the device consists of water dosing
syringe,
an
industrial
digital
temperature
controller,
a
consumer
ambient
digital
thermometer joined with relative humidity meter, a
chart recorder and a supply unit.
The core system can be heated to temperature
exceeding the room temperature or can be kept at
the room temperature to maintain the isothermal
working conditions.
At the beginning of the measurement, heat flow
value q’ho without a sample is saved. If water was
regularly distributed and the head temperature was
properly controlled the signal becomes quite
stable but will include some small turbulent
variations which cannot be avoided.
In the next step, the measuring head pulls down
and a sample is inserted between the head and the
cutout in the wind channel. Then the measuring
head moves back to the channel and squeezes the
sample. After short period when the signal reflects
the effect of different temperature of the sample,
the signal becomes steady and new value q’hs
which quantifies heat loses of moist measuring
head covered by a sample is read.
Relative water vapour permeability of the textile
sample rwv is calculated from the formula - Eq. 53:
rwv
q hs


100%
q h0

(53)
When the instrument should measure the water
vapour resistance according to the ISO 11092
Standard then a cellophane foil permeable for the
water-vapour but not permeable for the liquid
water is put to cover the head surface. Application
of the same procedure as above gives two values
q“h0 and q“hs.
The demanded water vapour resistance of the
sample Rwf then follows from the equation (54)
Rwf
 1
1
  pwv 
 pwv

 q

qh0
 hs
 2
-1

m

Pa

W




(54)
The values p“wv and pwv in this equation represent
the water vapour saturate partial pressure valid for
ambient temperature a and actual partial water
vapour pressure in a laboratory. Relative humidity
 expresses a relation between vapour densities
and also pres-sures
wv
pwv


wv
pwv


(55)
so the equation (55) is rewritten
Rwf
 1
1 
 ga  1    
 
q
 qh0
 
 hs
m
2
 Pa  W-1

(56)
using function p“wv = g(a) which is given in the
table of water vapour properties.
In the case of thermal resistance determination of
dry textile samples the whole procedure is
identical again but the measuring head is dry and
its temperature should be maintained at 32 C or
35 C that makes temperature difference to
ambient air .
The thermal resistance of the sample Rt then
yields the equation
 1
1 
Rt   


 qhs qh0 
K  m2  W-1 
(57)
5.4. Non- destructive testing of thermal comfort
properties of garments
Testing of thermohysiological properties of
protective clothing on thermal manniquins is the
ideal way of testing, but this procedure is very
costly. In some cases, we need to know or verify
just some specific fabric parameters like thermal
resistance or water vapour permeability. Classical
methods of testing, unfortunately, require cutting
of samples of certain dimensions, which results in
damaging the clothing. Fortunately, two relatively
new commercial instruments called ALAMBETA
and PERMETEST allow the non-destructive
determining of the above mentioned principal
comfort para-meters.
The commercial instruments called ALAMBETA
and
PERMETEST
for
the
evaluation
of
thermophysiological comfort of garments feature
special design of small sensitive elements, which
are surrounded by relative large isothermic areas
or by areas of constant humidity. This patented
solution avoids to some extent the so called edge
– effects and brings certain inde-pendence of the
measured results on the sample dimensions.
In practical tests, any part of the protective
garment can be inserted into the measuring zone
of the instruments, and the garment is not
damaged during the measurement. Naturally, the
results recorded on large garments may partially
differ from the results measured on standard
samples. That is why the second objective of the
paper is the analysis of the effect of sample
dimensions on the data determined by means of
the mentioned instruments.
The instrument is not delivered with any climatic
device, because its use under standard laboratory
conditions (at 22oC and relative humidity 55%)
offers reasonable precision of measurement.
Results of measurement are expressed in units
defined in the ISO Standard 11092.
5.4.1.Experimental results and their evaluation
Thermal resistance
All the samples were woven in plain weave and
composed of 100 % natural and synthetic polymers
in grey state. Their square mass varied from 125 to
160 g/m2. For thermal measurements, 9 different
samples was used, and the number of fabric layers
used in the measurement varied from single layers
up to 5 layers of fabrics.
COTTON - LARGE SAMPLES
THERMAL CONDUCTIVITY [mW/m.K]
THERMAL RESISTANCE [m2K/KW]
70
60
y = 11,853x + 40,807
R2 = 0,7464
50
40
lambda
r
30
20
y = 15,718x + 2,3825
R2 = 0,9995
10
0
0
0,5
1
THICKNESS h [mm]
1,5
2
COTTON - CUT SAMPLES
THERMAL CONDUCTIVITY [mW/m.K]
2
THERMAL RESISTANCE [m
K/KW]
70
60
y = 14x + 39,952
R2 = 0,8495
50
40
lambda
r
30
20
y = 14,8x + 2,9865
R2 = 0,9997
10
0
0
0,5
1
1,5
2
THICKNESS h [mm]
Figs 13 and 14 The effect of sample dimensions
on thermal resistance and conductivity of cotton
fabrics measured by means of the ALAMBETA
device
PES - CUT SAMPLES
THERMAL CONDUCTIVITY [mW/m.K ]
2
THERMAL RESISTANCE [m
K/KW ]
70
60
y = 10,506x + 42,565
R2 = 0,8024
50
40
lambda
r
30
20
y = 15,267x + 2,7071
R2 = 0,9994
10
0
0
0,5
1
THICKNESS h [mm]
1,5
2
large samples
THERMAL CONDUCTIVITY [mW/m.K]
2
THERMAL RESISTANCE [mK/KW]
70
60
y = 13,122x + 40,031
50
2
R = 0,9073
40
lambda
r
30
20
y = 14,445x + 3,1666
R2 = 0,9993
10
0
0
0,5
1
1,5
2
THICKNESS h [mm]
Figs 14 and 15 The effect of sample dimensions
on thermal resistance and conductivity of PES
fabrics measured by the ALAMBETA instrument
The first group of measurement embraced the so
called “cut” circular samples with the diameter
equal to the diameter of the instrument measuring
head (113 mm), whereas the second series of
measurement were performed on “endless” it
means very large fabrics.
All the samples were measured 5 times in different
places, and the CV values (%) were determined.
The detailed analysis reveals, that the differences
between thermal conductivity and thermal
resistance values for “cut” and “large” samples in
5 studied cases did not exceed 3%, in 2 cases 5%
and in the only case (for PAD 6) 9%. As regards
thermal resistance, even for 8 polymers, the
differences between cut and large samples were
lower than 3%, just for cotton sample the
discrepancy was 10 %. Variation coefficients in
most cases did not exceed 3%, hence, the
measurement seemed to be quite reliable. It can be
stated, that in all these cases, the suggested nondestructive measurements were reasonably
justified.
Water vapour permeability
The PERMETEST instrument requires samples,
which are larger then the diameter of wetted area
(60 mm in our case, but at new instruments it was
increased to 80 mm), due to fixing the sample in
circumferential clamps. To assure the defined
dimensions of the permeated area (to simulate the
cut samples), the fabric non-permeability was
achieved by means of printing of impermeable
polymer in the form of circle of diameter 60 mm.
Diameters of other circles were 80 mm, 100 mm
and the full large sample.
Water vapour relative permeability [%]
22,342
18,228
Ø 60 m m
Ø 80 m m
Ø 100 m m
large sam ple
14,114
10
100% PA
100% WO
100% CO
100% VI
100% PL
100% PP
Measured thin plain weaves of different composition
Fig16. The effect of sample dimensions on the
measured relative water vapour permeability of
thin woven fabrics similar in structure but
differing in composition
Experimental results in terms of relative water
vapour permeability (where 100% presents the
„permeability“ of free measuring surface) are
displayed in the next Fig.16. All the results present
the average values from 10 measurements on each
sample. Variation coefficients in most cases did
not exceed 5%, which confirms good measurement
precision for this kind of measurement.
From Fig. 16 follows, that the lowest levels of
permeability were found for samples of diameter
60 mm, which coincides with the wetted measuring
area of the instrument. If the sample dimensions
exceed the measuring area of the instrument, then
the determined water vapour permeability
increases by 4-9%. This effect can be explained by
planar conduction of condensed vapour from the
boundary of the measuring area towards fabric
edges. Lowest permeability increase (up to 6%), as
expected, was found for fabric made of common
synthetic polymers and blends.
The determined increase of water vapour
permeability is in most cases
small enough to permit the non-destructive
measurements of commercial textile products in
cases when customers require to confirm the
properties of their goods or for comparative tests
of various heavy fabrics also.
5.5. A new principle of evaluation of thermal
comfort of clothing based
on thermal mannequins, small thermal-comfort
instruments and data storage in PC
Thermal mannequin simulate a human body as a
thermal machine divided into up 17 independently
heated segments, which keeps (by means the PC
control) their surface (skin) temperature tS at the
average level of 33OC, and which enables exact
measurement of an electric power P [W] required
for this relatively truly simulation of heat
distribution in the human body. From these values,
the PC calculates the levels of individual
superficial heat fluxes qi of the mentioned
segments.
First, heat fluxes qin for the naked mannequin
should be measured and used for the calculation
of the exterior resistances REN of the naked body:
REN, i = (tSi - tE) / qN, I
(58)
In the next step, the mannequin is dressed and
total thermal resistances RTOT,,i will be determined
by similar procedure:
RTOT, i = (tSi - tE) / qTOT, I
(59)
The differences between the both above given
measurement present the demanded individual
clothing resistance levels
RCL, i = RTOT, i - REN, I
(60)
Up to this point, the common procedure was
described. Hes (1999) proposed to use in the next
step also small table instruments like ALAMBETA,
in order to determine the sum of thermal
resistance values of densely layered garments RG,i
covering without air gaps an individual segment of
thermal mannequin. The difference between RCL, i
and RG, i then will present the thermal resistance of
air gaps in clothing corresponding to individual
segment:
RA, i = RCL, i - RG, I
(61)
In the study made by Hes, Graveiro and
Gameiro (Coimbra 1998), the air layers under
absence of wind presented 22 - 40% of the full
women's clothing resistance (blouse, trousers) for
the standing mannequin. When air parallel flow
was included, the resistance of air gaps reached 35
- 65 % (thermal resistance of garments decreased).
For the sitting mannequin, the decrease of the
garment resistance due to the ventilation effects
was lower.
These values then correspond with certain (not too
high) precision to the chosen style, fit and size of
clothing system (suit). Presently, with the
advanced PC recording of all the data about
clothing manufacture, should be possible to find
the correlation procedure stored in PC, which
should enable the fast evaluation of thermal
resistance of selected clothing,
The input data will include, besides the proper
characteristics of the clothing style, fit and size,
also the thermal resistance values of individual
garments.
The effect of water vapour permeability of
garments on clothing comfort cannot be
determined directly by means of the described
thermal mannequin and the related procedure.
Fortunately, the processes of heat and vapour
transfer are similar. Therefore, once we know the
average thickness of the air gaps, and when we
can determine the water vapour permeability of
individual garments (e. g. by means of the
PERMETEST instrument),
it is relatively easy (for the specialist) to calculate
the total water vapour resistance of clothing,
following the rules given in Chapter 4.5.
Nevertheless, the effects concerning the moisture
condensation in garments and the generation of
moistening and absorption heat, cannot be
respected in such simplified procedure. Therefore,
in some countries, the sweating mannequins are
also used. However, the price of these thermophysiological:
Recording,
checking
and
investigation of the personal comfort simulators is
very high and the mannequin should be operated
by a skilled engineer.
5.6.Personal
thermo-physiological
comfort
sensoring chips worn under clothing or even
implanted
which
respond
on
external
radiofrequency inquiry.
Development project started at the Minho
University, Portugal. Objectives health and comfort
level during and after work and exercise. Analysis
of the effect of the clothing worn in real life
conditions on the personal comfort level. Long
time study of working conditions and lifestyle and
their influence on personal efficiency. Recorded
parameters: skin temperature, skin humidity, skin
surface heat flow, pulse.
6.Thermophysiological clothing comfort - design
6.1.Selected parameters of yarns and filaments,
which affect the thermo-physiological comfort of
fabrics
As already explained, fine surface fibres, even if
short, offer smooth and pleasant, but sometimes
too cool feeling, as well as and long smooth
surface fibres without any axial curling. Short
medium fineness surface fibres may provide
warmer feeling, but due totheir relative low
flexibility, they may scratch the skin (like
PES/cotton underwear). Why animal hairs, even if
long, give frequently warm and smooth feeling?
The animal hairs are frequently curly, and their
endings are tapered.
Therefore, the total contacting area is not large,
and the endings bend easily. Moreover, the surface
structure is irregular and contains a lot of pores.
Hairs also are not circular in their section. Any trial
to simulate the natural comfort feeling by means of
fabrics made of synthetic fibres should follow this
rules, e. g. by irregular yarn texturing, by irregular
yarn section and also by irregular surface raising.
If a special synthetic yarn consisting of continuous
filaments may contain filaments with very weak
places, which could be cut during an intensive
raising, then possibly a fabric surface may better
simulate the animal contact feeling.
6.2.The effect of chemical composition and
mechanical structure of shirt fabrics on
appearance and complex comfort properties of
shirts
6.3.Theory and design of ever-dry doublelayered fabrics composed of cotton and PP
textured filaments
Capillary pressure ΔP, causing the liquid
moisture flow generally form the big pores of the
equivalent radius R to small pores of the
equivalent radius r is proportional to the water
surface tension γand cosine function of the
contact angle Θ, according to the relation
ΔP = 2γ[(pr . cosΘr/ r) - pR . cosΘR/ R)]
(62)
Here, the term p presents the increase of the inner
surface of the capillary channel. If some fibre
surface treatment was achieved, which increases
the fibre roughness (like laser treatment), the
capillary pressure should increase and hence the
treated fabrics should exhibit higher wicking
properties.
As the general rule should be mentioned, that to
achieve the good wicking properties (high
moisture absorptivity), the yarn structure should
be compact and the space among the specially
profiled fibre section should be as small as
possible. The outer (cotton, viscose or at best
Lyocell fibre) layer should exhibit higher suction
force than the skin contacting (PP or special PES)
layer, but adhesion forces (cos Θ) in the skin
contacting layer should be lower.
Fig. 19 Examples of filaments (Moira TG 900,
Coolmax) creating small channels in twisted
bundles, which conduct moisture well
6.4.The use of Phase Changing Materials in
thermal protective clothing
Recently, sport clothes with higher thermal
capacity, which provide temporary protection
against overheating whether caused by stay in hot
surroundings or by higher production of metabolic
heat during high sport or work strain, appeared on
the world market. Protective function of those
products is based on heat absorption during phase
change in so called “phase change materials”
(PCM) which are put inside protection layer of the
special clothes.
Dynamics of fabric heating
While dressing especially of underwear with
temperature different from body temperature we
feel effect of heat accumulation in the clothes,
which is given by area related thermal capacity of
clothing C [J/m2] calculated as a product of
specific heat c [J/kg] and surface density of the
fabric M [kg/m2]. Thermal conductivity of textile
material takes share on the overall thermal-contact
perception of the fabric. Prof. Kawabata first
pointed out the importance of dynamics of
thermal-contact perception as a part of feel or
hand. Resulting parameter called thermal
absorbtivity b [Ws1/2/m2K] introduced by Hes can
be determined with commercial apparatus
ALAMBETA.
Thermal capacity of clothes has to defend the body
from sudden temperature changes in the
environment, for example when leaving airconditioned space and entering to tropical
atmosphere.
In fact, this balancing effect is weak and short.
Wool clothes provide much higher “buffer” effect
due to vaporization heat of absorbed water, but
only in case if high temperature of surrounding air
comes with low humidity. Yet this is not a usual
case. That is why fabrics based on heat
accumulation by means of phase change appeared
on the market.
This principle was first used in civil engineering under roofs of “intelligent” houses there were put
closed containers with PCM materials. The heat
accumulated during hot days warmed the whole
house during cold nights. Dr Barbara Pause
published this principle first after the suitable way
of application of these materials in fabrics was
solved. The mostly used materals - alkens - are
products of organic chemistry and their melting
temperature lies usually between 15 and 40oC. As
an example eicosan can be used, with melting
temperature 36,1oC.
Due to intensive marketing, these clothes are
known to public and they found their customers.
However, producers of the fabrics are not able to
characterize the effect of the proclaimed heat
protection in simple manner. There is growing
suspicion among textile specialists that the
protection is not necessarily proportional to high
price of these “performance” fabrics and
garments.
These wax-like materials are encapsulated in small
beads of micrometer range diameter and can be
deposited and fixed inside any textile structure
(e.g. in non-wovens) or on the fabric surface e.g.
by means of resins.
They exhibit relatively high phase change heat L
[J/m2 - when considering the concrete mass
applied in the textile layer] when they, due to
higher environmental temperature tE get melted, or
when they are subjected to cooling in the melted
state. In both cases, during the phase change time
τPC [sec], the PCM particles keep the textile layer
containing these particles on the phase change
temperature tPC for the period of tens of minutes. It
they are used e.g. for protection of the human skin
of temperature tS against hot environment (hot pot
when cooking) inside a protection glove,
consisting of 2 textile layers of interior and exterior
thermal resistances RP and RE with the PCM layer
is located between these layers,
then the protective function of such glove can be,
under certain simplifications and for RP >> RE,
analysed in the next rext.
Heat flow qo [W/m2] to the skin (tS  33C)
without protection:
qo = (tE – tS) / (RE + RPC+ RPROT)
(63)
Heat flow qp [W/m2] to the skin with protection
(tPC  35-38C):
qP = (tPC – tS) / (0,5 RPC +RPROT)
(64)
If PCM protection appears, then qP  qO,
Heat flow to PCM layer during the time of
protection OCH:
qPCM = (tE – tPC) /(0,5 RPC +RE)
(65)
Total heat L [J/m2] necessary for complete
melting of PCM layer:
L = qPCM  PC
(66)
Time of thermal protection provided e. g. by
protection glove determined under precondition (in
the practice only hardly feasible) that temperature
of PCM layer is for certain time in the whole PCM
layer constant:
PC = L / qPCM = L. RE / (tE – tPC)
(67)
From this simplified analysis follows that level of
protective function of PCM is strongly affected by
the level of phase change temperature and the
level of thermal resistance, and that the most
important factor is mass of PCM elements inserted
into active layer of clothes. If their weight portion
is low (lower than 30%), the outside penetrates
through the PCM layer to inside layers which are in
contact with skin and the second part of the
equation is invalid. To get really effective PCM heat
protection, we have to use thick textile layers,
which are less flexible and consequently less
comfortable.
New method for evaluation of thermal efficiency of
PCM protection
New instrument called PC Tester is in some extend
based on commer-cial equipment ALAMBETA for
the measurement of thermal-contact and thermal
thermal-isolation characteristic of fabrics - see Fig.
20:
Fig. 20 Scheme of the PC Tester instrument
The instrument consists of two blocks – boxes
with different temperatures. The temperature of the
first one, so called SKINBOX, is kept on skin
temperature tsk by means of classical circulation
thermostat 2. The second one is HOTBOX 3; it is
heated or cooled electrically. The temperature in
this case is kept by digital regulator or computer 4
on different level tE . Tested fabric 5 containing
PCM elements is located between sensing areas of
both boxes, and in the course of the testing
proccess it is surrounded by two flat textiles 6 and
7 which simulate both effect of thermal resistance
of underwear with respective air gaps RPROT and
effect of total thermal resistance RE between PCM
layer and the environment with temperature tE.
When evaluating effect of PCM layers it is
necessary to prepare the PCM layer with thermal
resistance RPC as well as the simulation layer with
the same thermal resistance RSIM, but without PCM
elements.
Evaluation of the efficiency is started by allocation
of layers 4, 5 (SIM) and 6 between sensing surfaces
of both boxes and their bringing into mutual
thermal contact. The computer begins to register
level of heat flow q[W/m2) passing through sensing
surface of the SKINBOX. As it is evident from Fig.
21, the heat flow reaches its maximum qmax0 in
short time 0 not exceeding several seconds,
because effective surface thermal capacity of
fabrics, given by product of specific heat c [J/kg]
and surface density of fabric [kg/m2] is very low.
The final value of thermal resistance is then given
by the relation (68).
In next step the textile fabric 5(SIM) replaces
protective layer 5(PCM) in the measured assembly
and measurement is repeated. In this case the
increase of the level of heat flow is slower,
because of the effect of heat accumulation needed
to accomplishing of the phase change. In theory,
the above mentioned accumulation of heat should
be constant for some time and consequently, the
heat flow should not change in the meaning of the
relation (68). Time of protection should be
characterized by the relation (66). In reality, there is
no “plateau” with constant value q at the
registration of the heat flow going though the
system with PCM layers, because PCM layer is not
continuous in usual application in textiles.
. A non reduced heat flow penetrates between
fibres from outside layer, and as a result of it the
curve of heat flow is smooth and continuous and
reminds again an exponential one. How can we
then simply evaluate time of protection?
In physics, the exponential curves characterize a
lot of natural processes, as e.g. radioactive isotope
decay. For simple expression of the radiation
intensity drop, the radioactive half time was
introduced, which is given by time necessary for
drop of radiate level intensity to half. This
parameter is useful, because it is clear for
understanding. Similarly, analogy of this parameter
will be used for evaluation of the thermal
protective efficiency of fabrics containing PCM
elements.
Fig. 21 Time course of heat flow passing through
the simulated skin during the evaluation of thermal
efficiency of PCM fabrics in the PC Tester
As the time of protection PC will be appointed
the time in which heat flow will be lower or equal to
one half of the maximum rate of heat flow qmax,o
achieved when measuring the fabric simulating the
protective layer, but without PCM elements.
Because thermal resistance R of fabrics is
given by the known relation
R = (tE – task) / q,
(68)
then the time of protection means in reality also
the time for what effective thermal resistance of
protective fabric is at least twofold in comparison
with the same layer without PCM elements.
Experimental results
First prototype of the equipment was made in
cooperation with Prof. R. Gomes at the University
of Minho. During the preliminary tests the PCM
layer (melting point 28°C) was surrounded by
textiles with the same thermal resistance R (about
0,1m2K/W) and the quantity of PCM elements was
raised from 0 to 50% of the sample weight. Time
necessary to reach the 50% level of qmax,o with
raising proportion of PCM was increasing almost
linearly to 620 sec, which in some extend proves
the validity of relation .
Another prototype of the device PCM tester was
build recently in the Textile Research Institute in
Taipei, Taiwan, and the method was once more
verified, by providing similar results. A priority of
the described method of evaluation of thermal
efficiency of PCM fabrics is covered by an US
patent since 2003.
6.5. Textiles changing their absorption of infrared
radiation heat according to the solar radiation level
Maximum level of heat flow coming from sun
(equator, midday, no clouds): 1400 W/m2. Solar
heat flow qS in warm countries (Portugal, Spain,
Italy) in summer midday: 900 W/m2
The heat flow reaching clothed person qSC depends
on the angle  between the rays and the line
perpendicular to the surface and then some part of
the flow is absorbed, some part reflected and the
rest passes though the clothing, according to the
next relation:
qSC = qS . cos  =  . qSC +  . qSC +  . qSC
(69)
Some liquid crystals dyestuffs or coatings are
black in the range from common comfort
temperatures till some temperature limit, e.g. 35OC.
Over the temperature limit, they turn grey and later
even white. Thus, their surface emissivity 
decreases, and the visible part of solar thermal
radiation gets reflected due to increased
reflectivity . The reduction of the absorbed
radiation flow may be up to 50%. Unfortunately,
these intelligent coatings are still quite expensive.
6.6.Application
of
semi-permeable
fabrics,
membranes and fabric coatings to achieve the
reasonable permeability for water vapour and
simultaneously no permeability for water drops.
The protection against wind also reduces
substantinally the heat loses by convection.
Intelligent breathable but waterproof fabrics
should allow to pass up to 2000-2500 g/m2 of
vaporized sweat per day at low physical activity
and up tp 4000-5000 g/m2/day at high energy
production. This water vapour permeability
naturally depends on the outer air relative humidity
and temperature.
Fig. 22 An example of the "windstopper" fabric,
NO WIND PRO 600
Fig. 23 Various forms of liquid water
Principal division of windproof and waterproof wv
permeable fabrics
1.dense woven fabric (up to 7000 yarns/cm), pore
size10-3m
made of mikrofibre yarns PES, PAD
2. coated basic material, microporous layer, pore
size 2-3m
·
by mechanical microperforation: direct or
indirect (crashed foam), coagulation procedure:
dry or wet
with hydrophilic coating, pore size
0,001m
3. lamination by membranes, which are
manufactured as folies
and fixed on basic woven material:
·
microporous, hydrophobic foils, pore size 30,1m
·
hydrophylic film, pore size 0,001m
Combination of both procedures. The membrane
can be also free. Laminates may constost of up to
3 layers.
Laminated fabrics should exhibit next thermal
comfort and wearing properties:

high water vapour permeability

low wind penetration

resistance against hydrostatic pressure (up to
15 m water column)

low garment mass

low bending and shearing rigidity, soft
handle.
Fig. 24 Measurement of windproof fabric surface
temperature by the IR camera. Without the
windstopper membrane the outer air cools the
jacket surface and its temperature is lower.
Also abrasion resistance is required, stability of
properties after repeated washing and washing
cleaning,
6.8.Military garments.
Overcoat "invisible" in visible light consists of
optical camera, which detects the image of the
background behind (in front of) of the wearer and
this image is projected on the special reflecting
garment in proper magnitude. Thus, when we
imagine an observer located in front of the
protected soldier, and watching him, the observer
should see the missing part of the background
projected on the soldier garment.
Current camouflage military garments for visible
and near infrared range
This garments offer certain invisibility in
homogeneous environment like forest, meadow or
desert, since their average emissivity corresponds
to the background. The applied NIR of personal
night vision systems was up to 1 micrometer, at
present the range increases till 1,2 micrometer.
Military garments invisible for low temperature
(medium infrared) detectors (detectors of own heat
radiation), due to very low surface emissivity.
Here, the total radiation heat flow (in spite of
higher body temperature compared with the
environment) is too weak to make difference
against the signal from the surroundings.
6.9.Examples of civic protective clothing against
high solar radiation
Clothing protecting against radiation heat should
prevent the passage of IR rays, but simultaneously
should allow the creation of the free convection
vertical streams in the clothing, which take away
the moisture and heated air. Thus, the clothing
should be bulky and porous in the space next to
skin, but external surface should be dense enough
to stop the solar radiation. Moreover, the body
motion should perform the pumping effect inside
the garment system, in order to take away the
stagnant humid air.
Indian sari is an example of such clothing. The
used special woven fabric is be very porous but
rigid, so that the fabric folds may create elastic air
channels which get deformed when walking. Also
Arabic burnus or Greek tunica satisfy most of the
above mentioned requirements. A new protective
clothing patented in Czech Republic exhibits,
except other features, many permanent vertical
channels, which support the intensive humid air
evacuation from the clothing.
7. SMART TEXTILES ( by Prof. L. Van Langenhove,
Univ. of Ghent)
Smart textiles are able to sense stimuli from the
environment, to react to them and adapt to them by
integration of functionalities in the textile
structure. The stimulus as well as the response
can have an electrical, thermal, chemical,
magnetic, or other origin.
Advanced materials, such as breathing, fireresistant or ultrastrong fabrics, are according to
this definition not considered as intelligent, no
matter how high-technological they might be.
The extent of intelligence can be divided in three
subgroups /5/:
passive smart textiles can only sense the
environment, they are sensors;
active smart textiles can sense the stimuli
from the environment and also react to them,
besides the sensor function, they also have an
actuator function;
finally, very smart textiles take a step further,
having the gift to adapt their behaviour to the
circumstances.
To fulfil the above presented tasks, two
components need to be present in the textile
structure in order to bear the full mark of smart
textiles: a sensor and an actuator, possibly
completed with a processing unit which drives the
actuator on the basis of the signals from the
sensor.
Although smart textiles find and will find
applications in numerous fields, this presentation
is limited to clothing. It involves for example
wearable smart textiles meant for medical
applications, designed to fulfil certain functions,
but apart from that without any fringes. Also
casual clothing is possible, which is expected to
be functional as well as fashionable. It also
embraces sports clothing, where the comfort
factor is even more critical. Finally, smart textiles
could be sold as a gadget, where the intelligent
character will be more accessory than useful but
in any case extremely visible.
Initially, smart clothing will find applications in
those fields where the need for monitoring and
actuation can be of vital importance, such as
medical environment, and with vulnerable
population groups, in space travel and the military.
However, as experience and and familiarity will
increase and hence breaking down barriers, the
field of application will in the long term definitely
widen to more daily applications such as sports
and leisure, the work environment and so on.
State of the art
The first generation of intelligent garments was
based on conventional materials and components
and garments were designed to fit in the external
elements. They can be considered as e-apparel,
where electronics are added to the textile. A first
successful step towards wearability was the ICD+
line at the end of the 90ies, which was the result of
co-operation between Levi´s and Philips. The
line´s coat architecture was adapted in such a
way that wxisting aparatuses could be put away in
the coat: a microphone, an earphone, a remote
control, a mobile phone and an MP3 player. The
coat construction at that time did require that all
these components, including the wiring,
were carefully removed from the coat before it
went into the washing machine. The limitation as
to maintenance caused a high need for futher
integration.
The most obvious thing to do was integrating the
connection wires of the different components into
the textile. To this end, conductive textile materials
are appealed to. Infineon has developed a
minituariased MP3 player, which can easily be
incorporated in a garment. The complete concept
consists of a central microchip, an earphone, a
battery, a download card for the music and an
interconnection of all these components through
woven conductive textiles. Robust and wash-proof
packing protects the different components.
No matter how strongly integrated, the functional
components remain non-textile elements, meaning
that maintenance and durability are still important
problems.
5 functions can be distinguished in an intelligent
suit, namely:
Sensors
Data processing
Actuators
Storage
Communication
They all have a clear role, although not all
intelligent suits will contain all functions. The
functions may be quite apparent, or may bean
intrinsic property of the material or structure. They
all require appropriate materials and structures,
and they must be compatible with the function of
the clothing: comfortable, durable, resistant to
regular textile maintenance processes and so on.
Sensors
Sensors detect certain signals and transform them
into another signals that can be read and
understood by a predefined reader, which can be a
real device or a person.
As for real devices, ultimately most signals are
being
transformed
into
electric
ones.
Electroconductive materials are consequently of
utmost importance with respect to intelligent
textiles.
When designing new textile sensors, the art will be
to specify the concepts of transformation that
make it possible to turn the signal one wants to
measure into (the variation of) a signal one can
measure (in most cases the latter will be an electric
signal). Possibly, intermediate transformations
may be necessary, although these must be
minimised.
Of course, apart from technical considerations,
concepts, materials, structures and treatments
must be focusing on the appropriateness for use in
or as a textile material. This includes criteria like
flexibility, water (laundry) resistance, durability
against deformation, radiation etc.
Nevertheless, when looking at possibilities of
transformation, e.g. from optical to electrical, from
thermal to mechanical, from mechanical to
electrical,
from
thermal
to
optical,
and
combinations of subsequent tranformations it will
be clear that there is an enormous potential of
sensors that are just waiting to be developed for a
huge range of textile applications.
Materials that have the capacity of such a
transformation are for instance:
●Thermocouple: from thermal to electrical
●The Softswitch technology: from mechanical
(pressure) to
electrical.
●It uses a so-called „Quantum Tunnelling
Composite (QTC)“. This composite has the
remarkable characteristic to be an isolator in its
normal condition and to change in a metal-like
conductor when pressure is being exercised on it.
Depending on the application the pressure
sensitivity can be adapted. Through the existing
production methods, the active polymer layer can
be applied on every textile structure, a knitted
fabric, a woven fabricm or a nonwoven. The
pressure sensitive textile material can be
connected to existing electronics.
●Fibre Bragg Grating (GBG) sensors: from
mechanical through optical to electrical. This is a
type of optical sensors receiving a lot of attention
the latest years. They are uswed for the
monitoring of the structureal condition of fibrereinforced composites, concrete constructions or
other construction materials. At the Hong Kong
Polytechnic Uniresity,
several important applications of optical fibres
have been developed for the measurement of
tension and temperature in composite materials
and other textile structures /4/. FBG sensors look
like normal optical fibres, but inside they contain at
a certain place a diffraction grid that reflects the
incident light at a certain wavelength (principle of
Bragg diffraction) in the direction where the light is
coming from. The value of this wavelength linearly
relates to a possible elongation or contraction of
the fibre. In this way, The Bragg sensor can
function as a sensor for deformation.
Data processing
Data processing is one of the components that are
required only when active processing is necessary.
So far, nop textile materials are available that can
perform this task. Pieces of electronics are still
necessary. However, they are available in
miniaturised and even in a flexible form.
Research is going on to fix the active components
on fibres (Ficom project). Many practical problems
need to be overcome before real computing fibres
will be on the market: fastness to washing,
deformation, interconnections, etc.
Actuators
Actuators respond to an impulse resulting from the
sensor function, possibly after data processing. In
a sense, actuators are similar to sensors in that
they also transform the impulse signal into a
response signal.
Actuators make thing move, they release
sunstances, make noise, and many others.
Shape memory materials are the best-known
examples in this area. They transform thermal
energy into motion. In a cold state, or beneath the
transition temperature, a shape memory alloy can
easily be deformed and the material will keep this
shape. If the material is heated above the transition
temperature, it will return to its original shape. The
material so to speak has „memorised“ this shape.
Because of its ability to react to a temperature
change, a shape memor alloy can be used as an
actuator and links up perfectly with the
requirements imposed to smart textiles. A common
shape memory alloy is Nitinol. It consists of a
mixture of nickel and titanium.
Shape memory alloys exist in the form of threads,
which makes them compatible with textile
materials. Although shape memory polymers are
cheaper, they are less frequently applied. This is
due to the fact that they cannot be loaded very
heavily during the recovery cycle.
Until now, few textile applications of shape
memory alloys are known. The Italian firm, Corpo
Nove, in cooperation with d´Appolonia, developed
the Oricalco Smart Shirt. The shape memory alloy
is woven with traditional textile material resulting
into a fabric with a pure textile aspect. The trained
memory shape is a straight thread. When heating,
all the creases in the fabris disappear. This means
that the shirt can be ironed with a hair dryer.
Real challenges in this area are the development of
very strong mechanical actuators that can act as
artificial
muscles.
Performant
muscle-like
materials, however, are not yet within reach.
●Materials that release subsrances already
have several comercial applications. However,
actively controlled release is not obvious.
Chemical products (in the widest sense) can be
released in a controlled wayusing two main
principles:
●Products are chemically bound to the substrate,
these bonds are broken down by a predetermined
factor, or
●The textile material contains one or many tanks
(massive fibre, micro or nanocapsules, micro or
nanopores) whereby release is controlled by an
intelligent barrier. Micro-encapsulation is a
wellknown example of this category.
Obviously, controlled release opens up a huge
number of applications as drug supply systems in
intelligent suits that can also make an
adequatediagnosis.
Mechanical and chemical actuators are clear
examples, but of course one can think of many
other types, again for a huge number of
applications.
Storage
Smart suits often need some storage capacity.
Storage of data or energy is most common.
Sensing,
data
processing,
actuation,
communication, they usually need energy, mostly
electrical power. Efficient energy management will
consist of an appropriate combination of energy
supply and energy storage capacity.
Energy supply is also based on transformation, in
this case of one type of energy into another one.
Sources of energy that are available to a garment
are for instance body heat, mechanical (elastic
from deformation of the fabrics, kinetic from body
motion), radiation, etc.
Infineon had the idea to transform the
temperature difference between the human body
and the environment into electrical energy by
means of thermogenerators. The prototype is a
rigid, thin micromodule that is discretely
incorporaed into the clothing. The module itself is
not manufactured out of textile material. However,
the line of thought is introduced.
The Infineon thermogenerator delivers 1,6
microwatt/cm2 and is washable thanks to plastic
packing.
The use of solar energy for energy supply is
also thought of. At the University of California,
Berkeley, a flexible solar cell is developed which
can be applied to any surface .
As mentioned before, energy supply must be
combined with energy storage. When hearing this,
one thinks of batteries. Batteries are becoming
increasingly smaller and lighter. Even flexible
versions are available, although less performant.
Currently, the lithium-ion batteries are found in
many applications.
Communication
For intelligent textiles, communication has many
faces:
commu-nication
may
be
required
-Within
one
element
of
a
suit,
-Between the individual elements within a suit,
-From the wearer to the suit to pass instructions,
-From the suit to the wearer or his environment to
pass
information.
Within the suit, communication is currently
realised by either optical fibres, eitherconductice
yarns. They both clearly have a textile nature and
can be built in the textile seamlessly, the
advantages and disadvantages of both carriers are
well known: optical fibres are light and insensitive
to EM radiation. The transport does not cause
production of heat. On the other hand, the signals
have to be transformed into electrical onesat least
in one point.
Communication with the wearer is possible for
instance by the following technologies:
For the development of a flexible textile
screen, the use of optical fibres is obvious as well.
France Telecom has managed to realise some
prototypes (a sweater and a backpack). At certain
points, the light from the fibre can come out and
form pixels on the textile surface. The textile
screen can emit static and dynamic colour images.
The resolution is extremely low however.
Nevertheless, in this way, these clothes are
uplifted to a first generation of graphical
communication means.
Pressure sensitive textuile materials allow
putting in information, provided a processing unit
can interpret the commands.
Communication with the wider environment does
not allow direct contact, so wireless connections
are required. This can be achieved by integrating
an atenna. The step was also taken to manufacture
his antenna in textile material. The advantage of
integrating antennas in clothing is that a large
surface can be used without the user being aware
of it. In the summer of 2002, a prototype was
presented by Philips Research Laboratories, UK
and Foster Miller, USA on the International
Interactive Textiles for the Warrior Conference
(Boston, USA). The researchers made use of
conductive yarn on the basis of copper and nylon.
Moreover, existing production methods
were
appealed to construct the textile antenna.
Requrement for further research
The potential of intelligent textiles is huge. One
can think of many applications for each of the
examples given above. The other way around,
starting from an application, the basic concepts
have to be defined and evaluated for their use in or
as a textile product. Selection of materials,
structure and production technology are the first
step in the design. The actual research phase will
be long and hard for many cases.
Basic items that need to be addressed to come to a
real breakthrough and to innovation are:
Transformation and conversion mechanisms;
New materials;
New structures that can offer the requested
function.
Conductive materials, and more specifically
inherently conducting polymers or ICPs, are
already being used in many applications: antistatic
working, EMI shielding, heating, transport of
electrical signals, etc.
These are fascinating, dynamic, molecular systems
suitable for applications in many domains of
intelligent clothing: polymer batteries, solar energy
conversion, biomechanical sensors, Some
materials are already available, be it at laboratory
level. Some substantial disadvantages, which have
to be overcome, are the instability of the polymer
in the air, the weak mechanical properties and the
difficult processing. However, in the United States
one has managed to spin the first polyaniline fibre.
Another class of materials that will play a major
role in many intelligent clothes are optical fibres.
They are well-known from application in
electronics, but the range of deformations to deal
with in textile applications is of a different order
and causes problems thar restrict the number of
applications at present.