Evaluation of the thermal comfort performance of
different knitted fabrics and fibre blends suitable for skin
layer of firefighters’ protective clothing
Nazia Nawaz, OlgaTroynikov
Royal Melbourne Institute of Technology, Australia
1Corresponding author: nazia.nawaz@student.rmit.edu.au
Introduction
Protective clothing is required to shield the wearers from a variety of
hazardous environments or extreme conditions encountered by humans in
some industries, military or firefighting.
Firefighters’ protective clothing
• Firefighters’ protective clothing plays a vital role for their protection against
heat, hot liquids, chemicals and mechanical impacts.
• The protective clothing facilitates the firefighter to approach the fire to
rescue people from fire and to fight the fire.
• Modern firefighters’ clothing is a multi-layered garment assembly which is
usually worn over an undergarment (skin layer).
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Firefighting and thermal comfort
• Firefighting is an exhaustive physical task which generates body heat, also in
addition extremely hot working environment results in substantial elevation of
body core temperature.
• To reduce that temperature to normal, the body perspires in liquid and vapour
form. For better control of body temperature in keeping it a normal level the
evaporation of perspiration is necessary.
• Thermal comfort of human body is maintained by perspiring both in vapour and
liquid form and moisture transmission through clothing has a great influence on
its thermal comfort
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Firefighting and thermal comfort
To provide thermal comfort to the human body the garment next to skin must
have three important attributes: to absorb
• Heat
• Vapour
• Liquid perspiration from skin and
then transfer these to the outside of the garment
Thermal comfort and fabric properties
Thermal comfort properties of textile fabrics are actually influenced by
• the type of fibre
• spinning method of yarns
• yarn count
• yarn twist
• yarn hairiness
• fabric thickness,
• fabric cover factor
• fabric porosity and finish
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Background
Milenkovic et al. (2009) demonstrated that fabric thickness, enclosed still air
and external air movement are the major factors that affect the heat transfer
through fabric.
Ozdil (2007) experimentally verified that yarn properties such as yarn count,
yarn twist and spinning process influence thermal comfort properties of 1×1 rib
knitted fabrics. He verified that,
• The 1 × 1 rib fabrics produced from finer yarns showed lower thermal
conductivity and higher water vapour permeability values than coarser
yarns counts.
• Combed yarn showed the higher water vapour permeability
• By increasing yarn twist used for 1 × 1 rib fabrics , thermal and water
vapour permeability of the fabrics was also increased.
• Thermal resistance values decreased as the twist coefficient of yarn
increased. Thermal resistance values of fabrics knitted with combed
cotton yarns were lower than the fabrics knitted with carded cotton yarns.
Milenkovic, L., Skundric, P., Sokolovic, R., Nikolic, T., (1999). "comfort Properties of Defence Protective clothing." The scientific Journal Facta
Universities 1(4): 101-106.
Özdil, N., A. MarmaralI, et al. (2007). "Effect of yarn properties on thermal comfort of knitted fabrics." International Journal of Thermal Sciences
46(12): 1318-1322.
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Background
Arzu Marmarali (2009) studied thermal comfort properties of blended yarns
and knitted fabrics of Cotton /Soybean fibres and Cotton/Seacell fibres in
different blend ratios and found that,
• The thermal resistance value of 100% cotton fabric was significantly
higher than whole blended materials.
• 50/50% blend ratio of both fabrics (Co/Seacell, Co/Soybean) had the
lowest thermal resistance values than the other blend ratios and that was
due to lower fabric thickness value of 50/50% Co/SeaCell and
Co/Soybean fabrics. Therefore with the decreasing of fabric thickness,
thermal resistance decreases.
Troynikov et.al (2011) studied moisture management properties of wool/
polyester and wool/bamboo knitted in single jersey fabrics for the
sportswear base layers and concluded that,
• Blending wool fibre with polyester fibre and, in particular, wool fibre with
regenerated bamboo fibre, improved moisture management properties
than fabrics in wool fibre or regenerated bamboo fibre without blending.
Troynikov, O., et all, Wiah, W., (2011). "Moisture management properties of wool/polyester and wool/bamboo knitted fabrics for sportswear base
layer." Textile Research Journal 0: 1-11.
Arzu Marmarali, M. B., Tuba Bedez Ute, Gozde Damci (2009). Thermal comfort Properties of Blended Yarns Knitted Fabrics. ITMC. Casablanca,
Morocco.
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Objective of the study
The Objective of present study is:
• To evaluate thermal and moisture management properties of six commercially
available knitted fabrics of different fibre blends and knitted structures for
skin layer garments of firefighter’s protective clothing
• The assessment and ranking of their thermal and moisture management
performance.
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Materials and methods
• Following are six commercially available knitted fabrics having different
fibre content and knit structure that were evaluated
• 100% Merino wool
• 60% Merino Wool/ 40% Bamboo
•100%Cotton
• 94% Merino wool/ 6% spandex
•100%Polyester
• 52% Merino wool / 48% Biophyl
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Fabric physical properties
• Fabric mass per unit area (gram / meter square)
• Fabric thickness (mm)
• Fabric density (No. of wales/cm and No. of courses/cm)
Fabric Moisture management properties
For evaluation of fabrics’ moisture management properties Moisture
Management Tester (MMT) was used according to American Association
of Textile Chemists and Colourists (AATCC) Test Method 195–2009.
Figure 1. Moisture management tester
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Figure 2. Schematic view of tester sensors
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Moisture management tester indices
A series of indexes are defined and calculated to characterize liquid
moisture management performance of the test sample by using moisture
management tester, which are as follow;
• Top wetting time WTt and bottom wetting time WTb
• Top absorption rate (ARt) and bottom absorption rate (ARb)
• Top max wetted radius (MWRt) and bottom max wetted radius (MWRb)
• Top spreading speed (SSt) and bottom spreading speed (SSb)
• Accumulative one-way transport index (AOTI) and overall moisture
management capacity (OMMC)
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Moisture management tester indices
The OMMC is an index indicating the overall capacity of the fabric to manage
the transport of liquid moisture, which includes three aspects
1. Average moisture absorption rate at the bottom surface
2. One-way liquid transport capacity
3. Maximum moisture spreading speed on the bottom surface
The larger the OMMC is the higher the overall moisture management ability of
the fabric is.
According to AATCC Test Method 195–2009, the indices are graded and
converted from value to grade based on a five grade scale (1–5). The five
grades of indices represent:
1 – Poor
2 – Fair
3 – Good
4 – Very good
5 – Excellent
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Table 1. Grading of MMT indices
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Fabric thermal properties (Thermal and water vapour resistance)
Thermal resistance and water vapour resistance of fabrics were
evaluated using sweating guarded hot plate according to ISO 11092.
Sweating guarded hot plate is able to simulate both heat and moisture
transfer from the body surface through the clothing layers to the
environment. It measures both the thermal resistance (insulation
value) and water vapour resistance of fabrics.
Figure 3. Sweating Guarded Hot Plate
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Figure 4. Schematic diagram of sweating guarded hot plate
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Fabrics’ thermal resistance
For the determination of thermal resistance of the sample, the air
temperature is set to 20 C and the relative humidity is controlled at 65%.
Air speed generated by the air flow hood is 1 m/s. After the system
reaches steady state, total thermal resistance of the fabric is governed by:
Rct  A(Ts  Ta) / H
(1)
Where,
Rct is the total thermal resistance plus the boundary air layer measured
in m² K/W,
A, the area of the test section in m²
Ts, the surface temperature of the plate in K
Ta, the temperature of ambient air in K
H, the electrical power in Watts
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Fabrics’ water vapour resistance
To measure the water vapour resistance of the fabric air temperature is set
at 35 C and relative humidity is controlled at 40%.After a steady state is
reached, the total evaporative resistance of the fabric is calculated by:
Re t  A( Ps  Pa) / H
(2)
Where,
Ret, is total vapour resistance provided by liquid barrier, fabric and
boundary air layer measured in m2KPa/W)
A, the area of test section in m2
Ps, the water vapour pressure at plate surface in Pa
Pa, the water vapour pressure of the air on Pa
H, the electrical power in Watts
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Results and discussion
Table 2. Physical and structural properties of sample fabrics
Fabric
code
Fibre
composition
Construction
Fabric
weight
(g/m2)
Fabric
thickness
(mm)
No. of
wales/c
m
No. of
courses
/cm
SJ1
100% Merino
wool
Single Jersey
139
0.35
18
18
SJ2
60% Merino
Wool/ 40%
Bamboo
Single Jersey
156
0.34
16
16
SJ3
100%Cotton
Single Jersey
149
0.47
19
15
SJ4
94% Merino
wool/ 6%
spandex
Single Jersey
185
0.55
20
20
IM1
100%Polyest
er
Interlock based mock mesh
168
0.61
16
16
IM2
52% Merino
wool / 48%
Biophyl
Interlock based mock mesh
216
0.97
16
12
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Results and discussion
Moisture Management Properties of sample fabrics
Table 3. MMT results in value
Fabric code
WTt
(sec)
WTb
(sec)
ARt
(%/sec)
ARb
(%/sec)
MWRt
(mm)
MWRb
(mm)
SSt
(mm/sec)
SSb
(mm/sec)
AOTI
(%)
OMMC
SJ1
CV
63.312
1.265
50.515
1.343
3.671
1.414
5.117
0.290
2.5
1.414
5
1.414
0.365
1.414
0.959
1.414
319.182
0.011
0.448
0.112
SJ2
CV
7.883
0.071
5.000
0.137
8.152
0.236
5.925
0.114
12.5
0.282
12.5
0.282
1.286
0.097
3.102
0.098
133.396
0.251
0.379
0.030
SJ3
CV
41.255
0.249
5.416
0.979
8.061
0.194
14.286
0.276
13.33
3
0.216
13.333
0.216
0.349
0.419
1.600
0.614
102.118
0.394
0.244
0.383
SJ4
CV
3.281
1.084
29.274
1.064
7.153
0.046
6.853
0.181
5
0
10
0
3.131
1.035
1.154
0.043
500.714
0.033
0.521
0.057
IM1
CV
30.617
1.165
47.063
1.242
39.894
0.953
5.200
0.548
7.5
0.471
7.5
0.471
0.947
1.280
0.941
1.329
102.399
0.283
0.203
0.397
IM2
CV
119.953
0
3.835
0.250
0
0
5.069
0.561
0
0
7.5
0.471
0
0
0.898
0.091
434.105
0.184
0.487
0.036
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Results and discussion
5
4
Grade
3
2
1
0
SJ1
SJ2
SJ3
SJ4
IM1
IM2
Top WTt Grade
2
3
2
4
2
1.5
Bottom WTb Grade
2
3.5
3.5
2
2
4
Figure 5. WTt and WTb grades of sample fabrics
3.5
3
2.5
Grade
2
1.5
1
0.5
0
SJ1
SJ2
SJ3
SJ4
IM1
IM2
Top ARt grade
1
1
1
1
3
1
Bottom ARb grade
1
1
2
1
1
1
Figure 6. ARt and ARb (%/sec) grades of sample fabrics
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Results and discussion
3.5
3
2.5
Grade
2
1.5
1
0.5
0
SJ1
SJ2
SJ3
SJ4
IM1
IM2
Top MWRt grade
1
2.5
3
1
1.5
1
Bottom MWRb grade
1
2.5
3
2
1.5
1.5
Figure 7. MWRt and MWRb (mm) grades of sample fabrics
4
3.5
3
Grade
2.5
2
1.5
1
0.5
0
SJ1
SJ2
SJ3
SJ4
IM1
IM2
Top SSt mm/sec grade
1
1.5
1
3.5
1
1
Bottom SSb mm/sec grade
1
3.5
2
2
1
1
Figure 8. SSt and SSb (mm/sec) grades of sample fabrics
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Results and discussion
6
5
Grade
4
3
2
1
0
SJ1
SJ2
SJ3
SJ4
IM1
IM2
AOTI %
4
3
3
5
3
5
OMMC
3
2
2
4
2
3
Figure 9. AOTI % and OMMC grades for sample fabrics
These results show that SJ1, SJ4 and IM2 have better moisture management
properties as compared to the other sample fabrics of the study. These three
fabrics are composed of 100% wool, wool/spandex and wool/biophyl and
having single jersey structures
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Results and discussion
Thermal properties (Thermal and vapour resistance)
Mean Rct
(m²K/W)
0.035
0.029
0.03
Mean Rct
0.025
0.02
0.015
0.01
0.011
0.009
0.008
0.007
SJ1
SJ2
SJ3
0.013
0.005
0
SJ4
IM1
IM2
Fabric code
Figure 10. Thermal resistance (Rct) of sample fabrics
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Results and discussion
Mean Ret
(m² Pa/W)
6
4.955
Mean Ret
5
4
3
2.093
1.994
2.123
SJ1
SJ2
SJ3
2.44
2.861
2
1
0
SJ4
IM1
IM2
Fabric code
Figure 11. Water vapour resistance (Ret) of sample fabrics
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Conclusion
The results and discussions demonstrate that
• wool and wool blends are the most suitable fabric to be used next to
skin to achieve thermal comfort
• The fibre content, fabric construction and fabric thickness influence
thermal comfort significantly.
Therefore it can be concluded that 100% wool and wool blends with
spandex and bamboo (SJ1, SJ2 and SJ4) in single jersey structure are more
suitable to use next to skin than SJ4, IM1 and IM2.
100% cotton in single jersey structure can also be a good choice because it
has lower thermal and water vapour resistance like SJ1, SJ2, and SJ3 but
not in extremely hot environments like firefighting where body perspires
heavily in liquid form and cotton is unable to provide better liquid moisture
transfer properties like wool and wool blends to keep skin dry.
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