It’s A Wrap
“Best Buy” Science Experiments
Dr. Marialice Curran, EDUC 555/Fall 2012
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Which Plastic Wrap is the “Best Buy”?
PURPOSE:
The objective of this investigation is to compare, through scientific testing, which of three
plastic wraps performs best overall.
RATIONALE:
My 12-year old daughter and I frequently cook and bake together. In the process, we are
always in need of plastic wrap to keep our food products fresh. As I don’t always buy the same
brand of plastic wrap, we have used several products and discovered that different brands of
plastic wrap perform differently under certain conditions and circumstances. For example,
some plastic wraps seem to adhere well to certain surfaces; some are stronger and can hold the
weight of other food items stacked directly on top of them; and finally, some seem to form a
better seal and keep food fresher. The following experiments were designed to investigate
which of three different brands of plastic wrap performed “best” in three specific tests. All
three brands were purchased from the Stop & Shop in Enfield, CT.
My daughter and I investigated the following:
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Saran Wrap – best-selling brand, also most expensive of the three
Glad Wrap – well-known brand; second most expensive
Stop & Shop – “house brand”, least expensive
GENERAL BACKGROUND ON PLASTIC WRAP:
According to www.answers.com, plastic wrap is a form of food packaging consisting of a thin
film of flexible, transparent polymer that clings to itself and to food containers to form a tight
seal. The plastic keeps food fresh by protecting it from air and by preventing either the loss, or
the absorption of moisture in foods.
In scientific terms, plastics are artificial polymers made by humans, not nature. They consist of
gigantic molecules formed by combining thousands of small molecules (monomers) of the same
kind into a long chain. This process is called polymerization. (Natural polymers also exist and
include silk, rubber, and cotton.)
Plastic wrap is made when granules of plastic are heated and forced through a die to form a
tube of stretchable plastic in a process known as extrusion. Air is blown onto the moving plastic
to stretch the plastic to the desired thinness and metal rollers roll the plastic into a film.
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Concerns about using plastic wrap to protect food are that it is difficult to recycle and is seldom
reused, and that certain plasticizers used as additives can be harmful, especially the wrap is
used to heat food in the microwave.
BACKGROUND ON 3 SPECIFIC PRODUCTS TO BE TESTED:
“Consumer plastic wraps are made from three major categories of plastics: polyethylene (PE),
polyvinylidene (PVDC) and polyvinyl chloride (PVC).” (www.edusite.com/science/products.htm).
The three products we chose to test represent each of these categories:
Saran Wrap – Originally made of Polyvinyliden chloride (PVDC) which was discovered at Dow
Chemical in Michigan in 1933 by mistake in the process of developing a dry cleaning product. It
was initially developed into a spray to protect US fighter planes and automobile upholstery
from the elements. In 1942 Dow’s PVDC was woven into ventilated mesh for use in soldiers’
combat boots. It was formed into a thin clingy film and introduced as Saran (the combination of
the first names - Sarah and Anne - of the principal investigator’s wife and daughter) in 1949. It
quickly became popular for its ability to preserve the flavor and aroma of food items stored in
the refrigerator. Principal advantages were: low permeability to water vapor, flavor and aroma
molecules as compared with other plastics; slowed food spoilage and locked in flavor. PVDC is
not naturally flexible and must have plasticizers added or it is hard and rigid. Interestingly,
today’s Saran Wrap is no longer composed of PVDC, but is made of low density polyethylene
(LDPE) which is cheaper, easier to manufacture and recycle, and safer, due to fewer plasticizer
additives. LDPE is impermeable but has far less cling than before.
Glad Wrap –Made from polyethylene (PE) which is naturally flexible, with a stickifier added for
extra hold. It was invented in Australia by a Union Carbide Corporation’s chief research chemist
there and introduced to the US market in 1963 as a competing food wrap. It contains no
plasticizers. It is considered impermeable but not very clingy.
Stop & Shop Plastic Wrap – Made of a “food-safe version” of PVC (closer to PVDC) a blending of
special plastic resins with plasticizers to provide softness and cling to its naturally rigid nature. It
is similar to Stretch-tite Premium Plastic Food Wrap which is used by many restaurants and
professional food producers. The original formula of PVC was produced before World War II as
a second-rate substitute for rubber, but not utilized as a protective film until the 1950’s. It was
prized for its high clingability, but plasticizers and chlorine in these wraps held a risk of food
contamination, so manufacturers came up with safer substitutes. According to
(www.bestcovery.com), it doesn’t keep food quite as fresh as Glad Cling Wrap, but testers
named it tops in toughness and clinginess. Some consumers are still wary that any form of PVC
may not be as safe as other materials, but like that it is heavy duty and clings well.
VARIABLES/PRODUCT CHARACTERISTICS TO TEST:
Strength: How much weight/pressure can plastic wrap withstand before tearing?
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Cling/Adhesion: How well does plastic wrap adhere to 3 materials: glass, plastic and paper
Sealing Ability: How well does plastic wrap prevent moisture evaporation, keeping food fresh?
Although there are numerous other brands of plastic film readily available in grocery stores, we
selected these three products because we wanted to test the two most popular, heavily
advertised, and competing brands against each other, and against a cheaper, less known,
generic brand. By gauging performance in the three qualities that define the purpose of plastic
wrap (strength, stickiness, and sealing); we hope to identify the “Best Buy” for consumers.
Price is an interesting factor, but not one of our test considerations.
HYPOTHESIS:
Prior to beginning experimentation, we did conduct some online research on the three major
categories of plastics -- polyethylene (PE); polyvinylidene (PVDC, now LDPE); and polyvinyl
chloride (revised PVC). According to studies by Cook’s Country, the major difference between
PVC/PVDC and LDPE is that the former (Stop & Shop) clings better. LDPE (Saran) is less
permeable, which means that food should stay fresher with less odor transference, but doesn’t
cling as well, even though polymers can be added to help “cling”. Polyethylene (Glad) is very
safe as far as reheating and general food safety but not rated highest in tests comparing
clinginess.
Given these facts, it is reasonable to suppose that the Stop & Shop brand should do well in the
cling/adhesion test, Saran should be better in locking in moisture and freshness, and that Glad
should be average in all areas. I am wondering that if popularity and price (you get what you
pay for) are factored in, maybe I should conclude that Stop & Shop, the cheapest brand, cannot
perform as well as its two, better known, more expensive, competitors.
PREDICTION:
Based on our research, my daughter and I predict that there may be split results based on the
three tests, depending largely on the type of plastic that each brand is made of. However, we
give an overall edge to Saran Wrap, which as the most established brand in the United States,
must have built a reputation on earned results.
PROCEDURE:
Three experiments were designed for classroom use. Three trials were performed for each.
Test #1: Strength: How strong is the plastic wrap? Which brand holds the most weight until it
rips?
Test #2: Stickability: How well does the brand adhere to three 3 surfaces, commonly found in
the home: glass, paper, and plastic?
Test #3: Permeability:
(3a) how well does the plastic wrap trap water vapor; keeping moisture in?
(3b) How well does it keep actual food “fresh”?
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COMPLETE LIST OF MATERIALS: 25 students (8 groups of 3 and one group of 4)
Test #1:
8 glass 750 ml (3 cup) Pyrex bowls
8 paper “gift” bags (square-bottomed, 8 mm x 21 mm, 30 gram)
24 (3 sheets x 8 teams) 20 mm or 8 inch squares of Saran Wrap (for 3 trials)
24 (3 sheets x 8 teams) 20 mm or 8 inch squares of Glad Plastic Wrap (for 3 trials)
24 (3 sheets x 8 teams) 20 mm or 8 inch squares of Stop & Shop Wrap (for 3 trials)
Adhesive labels ( 3 color ½ in round dot)
Black marker
8 (0.25 in or¼ inch wide rubber bands
16 boxes (100 count) of ½ USS Flat Washers (Hot Tip Galvanized); each washer weighs 28g/1 oz
Kitchen or bathroom scale
Test #2:
8 (16 oz or 453.59237 g) clear/hard plastic drinking cups
8 (16 oz or 453.59237 g) paper drinking cups
8 (16 oz or 453.59237 g) glass drinking cups
24 (3 sheets x 8 teams) 15 mm or 6 inch squares of Saran Plastic Wrap (3 trials)
24 (3 sheets x 8 teams) 15 mm or 6 inch squares of Glad Plastic Wrap (3 trials)
24 (3 sheets x 8 teams) 15 mm or 6 inch squares of Stop & Shop Plastic Wrap (3 trials)
8 bags (12.60 oz or 357.2 g) M&M milk chocolate candies
8 sets measuring cups (1/4 cup or 2 oz. or 56.699046 g); ½ cup or 4 oz. or 113.39809 g; 1 cup or
8 oz. or 226.79618 g)
8 plastic or paper bowls
Adhesive labels ( 3 color ½ in round dot)
Black marker
Test #3 (two tests):
3a)
8 apples (cut into 12 equal pieces)
24 (3 sheets x 8 teams) 15 mm squares of Saran Plastic Wrap
24 (3 sheets x 8 teams) 15 mm squares of Glad Plastic Wrap
24 (3 sheets x 8 teams) 15 mm squares of Stop & Shop Plastic Wrap
Adhesive labels ( 3 color ½ in round dot)
Black Marker
8 foil baking sheets (15 -3/32 x 10-15/16 inches or 383.38125 x 277.8125 mm)
3b)
72 plastic cups (9 glasses x 8 teams) ( 354.8 mil or 12 oz)
8 measuring cups (56.699046 g or 2 oz or ¼ cup)
24 (3 sheets x 8 teams) 15 mm or 6 inch squares of Saran Plastic Wrap
24 (3 sheets x 8 teams) 15 mm or 6 inch squares of Glad Plastic Wrap
24 (3 sheets x 8 teams) 15 mm or 6 inch squares of Stop & Shop Plastic Wrap
Adhesive labels ( 3 color ½ in round dot)
8 foil baking sheets (15 -3/32 x 10-15/16 inches or 383.38125 x 277.8125 mm)
Bottled Water
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DATA/OBSERVATIONS:
Test #1 –Strength
Procedure Instructions For Each Team:
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Safety Procedures: Closed toe shoes worn for protection from weighted objects.
9 Squares of 20 mm plastic are gathered and labeled for three trials each of the three
brands of plastic wrap. (3 with red dot/labeled S for Saran with black marker; 3 with
blue dot/labeled G for Glad; 3 with yellow dot/labeled S&S for Stop & Shop)
One 750ml Pyrex bowl is the base for stretching the plastic wrap; used for all nine trials.
To begin, one 20mm square of Saran Wrap is tautly stretched over the top of the bowl
and secured with the rubber band.
The paper gift bag is carefully placed on top of the stretched plastic wrap. (Note: the bag
is necessary to hold a larger quantity of washers).
Washers (each weighs 28 g/1 oz) are added, one-at-a-time, to the bag and counted.
When enough weight from the washers in the bag forces the plastic film to burst or rip,
the bag is removed and the washers are recounted for accuracy (if necessary).
Process is repeated for 2nd and 3rd trials of Saran Wrap and data recorded.
Process continues using the 3 squares of Glad Wrap (3 separate trials); results are
recorded.
Process continues using the 3 squares of Stop & Shop Plastic Wrap (3 separate trials);
results are recorded.
Weight recorded for each brand in its three trials subtracts the weight of the paper gift
bag (30 grams/1 oz)
Test # 2: Stickability
Procedure Instructions for Each Team:
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No specific safety concerns
9 Squares of 20 mm plastic are gathered and labeled for three trials each of the three
brands of plastic wrap. (3 with red dot/labeled S for Saran with black marker; 3 with
blue dot/labeled G for Glad; 3 with yellow dot/labeled S&S for Stop & Shop)
Glass Test: 3 glasses (16 oz or 453.59237g) are lined up on work table.
Measure 1/4 cup or 2 oz. or 56.699046 g of M&M milk chocolate candies and place in
first glass.
Place I square of Saran Wrap on glass (with M&Ms inside) and press down firmly all
around rim and sides of glass.
Position a plastic or paper bowl under glass to catch candies when glass is inverted.
Invert glass for 5 seconds; record whether plastic holds M&Ms inside glass or releases
them into bowl. Using the same first glass, repeat process two more times and record
results.
Next, measure ½ cup or 4 oz. or 113.39809 g of M&M candies into same first glass. Use
same Saran Wrap square as above (pressing down firmly all around rim and sides of
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glass). Position bowl and invert glass as before for 5 seconds. Record results. Repeat
process two more times and record results.
Measure 1 cup or 8 oz. or 226.79618 g of M&Ms into same glass as above. Use same
Saran Wrap square as above (pressing down firmly all around rim and sides of glass).
Position bowl and invert glass as before for 5 seconds. Record results. Repeat process
two more times and record results. (You are done with this first glass).
Take 2nd glass and place I square of Glad Wrap on glass (with M&Ms inside) and press
down firmly all around rim and sides of glass.
Position a plastic or paper bowl under glass to catch candies when glass is inverted.
Invert glass for 5 seconds; record whether plastic holds M&Ms inside glass or releases
them into bowl. Repeat process two more times and record results.
Next, measure ½ cup or 4 oz. or 113.39809 g of M&M candies into same second glass.
Use same Glad Wrap square as above (pressing down firmly all around rim and sides of
glass). Position bowl and invert glass as before for 5 seconds. Record results. Repeat
process two more times and record results.
Measure 1 cup or 8 oz. or 226.79618 g of M&Ms into same glass as above. Use same
Glad Wrap square as above (pressing down firmly all around rim and sides of glass).
Position bowl and invert glass as before for 5 seconds. Record results. Repeat process
two more times and record results. (You are done with the second glass).
Measure 1/4 cup or 2 oz. or 56.699046 g of M&M milk chocolate candies and place in
third glass.
Place I square of Stop & Shop Wrap on third glass (with M&Ms inside) and press down
firmly all around rim and sides of glass.
Position a plastic or paper bowl under glass to catch candies when glass is inverted.
Invert glass for 5 seconds; record whether plastic holds M&Ms inside glass or releases
them into bowl. Repeat process two more times and record results.
Next, measure ½ cup or 4 oz. or 113.39809 g of M&M candies into same third glass. Use
same Stop & Shop Wrap square as above (pressing down firmly all around rim and sides
of glass). Position bowl and invert glass as before for 5 seconds. Record results. Repeat
process two more times and record results.
Measure 1 cup or 8 oz. or 226.79618 g of M&Ms into same glass as above. Use same
Stop & Shop Wrap square as above (pressing down firmly all around rim and sides of
glass). Position bowl and invert glass as before for 5 seconds. Record results. Repeat
process two more times and record results. (You are done with the glasses).
Paper Cup Test: 3 paper cups (16 oz or 453.59237g) are lined up on work table.
Measure 1/4 cup or 2 oz. or 56.699046 g of M&M milk chocolate candies and place in
first paper cup.
Place I square of Saran Wrap on glass (with M&Ms inside) and press down firmly all
around rim and sides of paper cup.
Position a plastic or paper bowl under paper cup to catch candies when inverted.
Invert paper cup for 5 seconds; record whether plastic holds M&Ms inside cup or
releases them into bowl. Using the same paper cup, repeat process two more times and
record results.
Next, measure ½ cup or 4 oz. or 113.39809 g of M&M candies into same first paper cup.
Use same Saran Wrap square as above (pressing down firmly all around rim and sides of
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cup). Position bowl and invert as before for 5 seconds. Record results. Repeat process
two more times and record results.
Measure 1 cup or 8 oz. or 226.79618 g of M&Ms into same paper cup as above. Use
same Saran Wrap square as above (pressing down firmly all around rim and sides of
cup). Position bowl and invert as before for 5 seconds. Record results. Repeat process
two more times and record results. (You are done with this first paper cup).
Take 2nd paper cup and place I square of Glad Wrap on cup (with M&Ms inside) and
press down firmly all around rim and sides.
Position a plastic or paper bowl under glass to catch candies when cup is inverted.
Invert cup for 5 seconds; record whether plastic holds M&Ms inside or releases them
into bowl. Repeat process two more times and record results.
Next, measure ½ cup or 4 oz. or 113.39809 g of M&M candies into same second paper
cup. Use same Glad Wrap square as above (pressing down firmly all around rim and
sides). Position bowl and invert as before for 5 seconds. Record results. Repeat process
two more times and record results.
Measure 1 cup or 8 oz. or 226.79618 g of M&Ms into same paper cup as above. Use
same Glad Wrap square (pressing down firmly all around rim and sides). Position bowl
and invert cup as before for 5 seconds. Record results. Repeat process two more times
and record results. (You are done with the second paper cup).
Measure 1/4 cup or 2 oz. or 56.699046 g of M&M milk chocolate candies and place in
third paper cup.
Place I square of Stop & Shop Wrap on third cup (with M&Ms inside) and press down
firmly all around rim and sides.
Position a plastic or paper bowl to catch candies when cup is inverted.
Invert cup for 5 seconds; record whether plastic wrap holds M&Ms inside cup or
releases them into bowl. Repeat process two more times and record results.
Next, measure ½ cup or 4 oz. or 113.39809 g of M&M candies into same third cup. Use
same Stop & Shop Wrap square as above (pressing down firmly all around rim and
sides). Position bowl and invert as before for 5 seconds. Record results. Repeat process
two more times and record results.
Measure 1 cup or 8 oz. or 226.79618 g of M&Ms into same cup as above. Use same Stop
& Shop Wrap square as above (pressing down firmly all around rim and sides). Position
bowl and invert cup as before for 5 seconds. Record results. Repeat process two more
times and record results. (You are done with the paper cups).
Clear/Hard Plastic Cups: 3 plastic cups (16 oz or 453.59237g) are lined up on work table.
Measure 1/4 cup or 2 oz. or 56.699046 g of M&M milk chocolate candies and place in
first plastic cup.
Place I square of Saran Wrap on plastic cup (with M&Ms inside) and press down firmly
all around rim and sides.
Position a plastic or paper bowl to catch candies when inverted.
Invert plastic cup for 5 seconds; record whether plastic wrap holds M&Ms inside cup or
releases them into bowl. Using the same cup, repeat process two more times and
record results.
Next, measure ½ cup or 4 oz. or 113.39809 g of M&M candies into same first plastic cup.
Use same Saran Wrap square as above (pressing down firmly all around rim and sides of
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cup). Position bowl and invert as before for 5 seconds. Record results. Repeat process
two more times and record results.
Measure 1 cup or 8 oz. or 226.79618 g of M&Ms into same plastic cup as above. Use
same Saran Wrap square as above (pressing down firmly all around rim and sides of
cup). Position bowl and invert as before for 5 seconds. Record results. Repeat process
two more times and record results. (You are done with this first plastic cup).
Take 2nd plastic cup and place I square of Glad Wrap on cup (with M&Ms inside) and
press down firmly all around rim and sides.
Position a plastic or paper bowl to catch candies when cup is inverted.
Invert cup for 5 seconds; record whether plastic holds M&Ms inside or releases them
into bowl. Repeat process two more times and record results.
Next, measure ½ cup or 4 oz. or 113.39809 g of M&M candies into same second plastic
cup. Use same Glad Wrap square as above (pressing down firmly all around rim and
sides). Position bowl and invert as before for 5 seconds. Record results. Repeat process
two more times and record results.
Measure 1 cup or 8 oz. or 226.79618 g of M&Ms into same plastic cup as above. Use
same Glad Wrap square (pressing down firmly all around rim and sides). Position bowl
and invert cup as before for 5 seconds. Record results. Repeat process two more times
and record results. (You are done with the second plastic cup).
Measure 1/4 cup or 2 oz. or 56.699046 g of M&M milk chocolate candies and place in
third plastic cup.
Place I square of Stop & Shop Wrap on third cup (with M&Ms inside) and press down
firmly all around rim and sides.
Position a plastic or paper bowl to catch candies when cup is inverted.
Invert cup for 5 seconds; record whether plastic wrap holds M&Ms inside cup or
releases them into bowl. Repeat process two more times and record results.
Next, measure ½ cup or 4 oz. or 113.39809 g of M&M candies into same third cup. Use
same Stop & Shop Wrap square as above (pressing down firmly all around rim and
sides). Position bowl and invert as before for 5 seconds. Record results. Repeat process
two more times and record results.
Measure 1 cup or 8 oz. or 226.79618 g of M&Ms into same cup as above. Use same Stop
& Shop Wrap square as above (pressing down firmly all around rim and sides). Position
bowl and invert cup as before for 5 seconds. Record results. Repeat process two more
times and record results. (You are done with the plastic cups).
Test #3: Permeability:
(3a) how well does it keep food “fresh”?
Procedure Instructions for Each Team:
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No specific safety concerns if teacher uses knife to cut apple slices
One apple is cut into 12 equal slices
Label 9 (15 mm) squares (3 with red dot/labeled S for Saran with black marker; 3 with
blue dot/labeled G for Glad; 3 with yellow dot/labeled S&S for Stop & Shop) and adhere
labels to plastic wrap.
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On foil baking sheet line up: 3 unwrapped apple slices (control group); 3 slices wrapped
tightly with Saran; 3 slices wrapped tightly with Glad; 3 slices wrapped tightly with Stop
& Shop.
Check color/condition of apples after one hour; after one day. Record results.
(3b) how well does the plastic wrap trap water vapor (which preserves freshness in food).
Procedure Instructions for Each Team:
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No specific safety concerns
Label 9 (15 mm) squares (3 with red dot/labeled S for Saran with black marker; 3 with
blue dot/labeled G for Glad; 3 with yellow dot/labeled S&S for Stop & Shop) and adhere
labels to plastic wrap.
On foil baking sheet line up nine cups. Measure and pour ¼ cup of water into each cup.
Cover 3 with Saran; 3 with Glad; 3 with Stop & Shop. Place rubber band around rim of
each cup to secure.
Mark water line on each plastic cup with marker.
Check for water vapor droplets on plastic cover or sides of glass after one hour; after
one day. Record results.
After one day, observe water line on each cup. Record results.
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DATA/OBSERVATIONS
Test #1– Weight Resistance/Strength – measured by number of 28g /1 oz. washers added until
plastic breaks, rips or pops
Trial Test #
SARAN WRAP GLAD WRAP STOP & SHOP WRAP
#1
236
188
240
#2
240
204
230
#3
238
220
246
# of Washers: 714
612
716
Observations: We had a difficult time determining what type of weighted object to use for this
test – small, flat and heavy. Research online proved that this is a problem for professional and
Science Fair scientists worldwide! Marbles rolled off the top of the plastic film after a medium
number were added; heavy bolts with grooves tore the plastic; coins were considered but
would have been needed in a very large quantity. The biggest problem was finding any object in
large enough quantities. My eldest son, a carpenter, solved the problem by providing us with
boxes of flat metal washers.
In our testing, we were surprised to discover that plastic wrap stretched taut over a bowl and
secured with a rubber proved to have a great amount of tensile strength. Therefore, a second
problem that arose and needed to be solved before testing, was how to hold the great number
of small objects in contact with the plastic film top. For this we used a tall, paper gift bag, which
sat on top of the plastic-covered bowl. Washers were dropped into the bag, one at a time.
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Test #2 – Stickability –
 How does the plastic wrap adhere to the three 3 different surfaces of glass, paper and
plastic?
 How does the plastic wrap hold M&M milk chocolates:
¼ cup/2 oz./56.699046g
½ cup/4 oz./113.39809g
1 cup/8 oz./226.79618g
Trial #1:
Saran Wrap
Container Material
glass
paper
plastic
Holds: ¼ cup
yes
no
yes
Holds: ½ cup
yes
no
yes
Holds: 1 cup
yes
no
no
Holds: ¼ cup
yes
no
no
Holds: ½ cup
yes
no
no
Holds: 1 cup
yes
no
no
Holds: ¼ cup
yes
no
yes
Holds: ½ cup
yes
no
yes
Holds: 1 cup
yes
no
yes
Glad Wrap
Container Material
glass
paper
plastic
Stop & Shop
Container Material
glass
paper
plastic
Trial #2: Same result
Trial #3: Same result
Observations: We had purchased and planned to use plastic, paper and glass bowls of the same
size and shape for this test, but discovered that there was no way to hold the bowl upside
down, as necessary for this test, and not interfere with the plastic wrap that overlapped the
sides of the bowl. For example, we seemed to either give unfair advantage by holding onto the
plastic wrap, or put the plastic wrap at a disadvantage by breaking its seal with our fingers. This
was solved by switching to drinking cups made of the three specified materials, which had
enough room to seal with plastic at the top and hold near the middle or bottom of the glass.
Prior to beginning our experiment, we had researched online about the fact that plastic wrap
molecules are long and tightly coiled, but when pulled, their molecules stretch. Friction created
allows plastic wrap to absorb an electric charge. Electrons scatter, causing a negative charge.
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The surface covered with the wrap is positively charged, thus the “CLING”…opposites attract!
However, cling depends on the amount of charge in the container and its covering; some
materials cling, some do not.
Our most obvious observation was that paper does not create enough of a charge to cling to
any of the three brands of plastic wrap that we tested. It would be interesting to research this
more and find out if paper product can ever effectively seal with plastic wrap.
Test # 3 - Permeability:
(3a) How well does the plastic wrap trap water vapor. ¼ cup/2 oz./56.699046g added to each
of nine glasses and marked with marker on side. Checked after 1 day.
Change in water level:
Discernible change
Very slight change
No change
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Heavy water
beading on
inside top &
sides
Saran Wrap (3 trials)
Light water
beading on
inside top &
sides
Glad Wrap (3 trials)
No water
seen on
inside top or
on sides
Stop & Shop (3 trials)
(3b) How well does it keep food “fresh”, keep moisture in and prevent apple from turning
brown? Results checked after 1 day.
Trial #1
Control Group (no plastic wrap):
overall brown with slight withering around edges –
Saran Wrap:
overall brown—no change in apple shape
Glad Wrap:
lightest color change –, no change in apple shape
Stop & Shop Wrap:
medium color change –, no change in apple shape
80% browning
60% browning,
20% browning
40% browning
Trial #2
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Control Group (no plastic wrap):
overall brown with slight withering around edges –
Saran Wrap:
overall brown—
Glad Wrap:
lightest color change –
Stop & Shop Wrap:
medium color change –
60% browning
40% browning
10% browning
30% browning
Trial #3
Control Group (no plastic wrap):
overall brown with slight withering around edges –
Saran Wrap:
overall brown—
Glad Wrap:
lightest color change –
Stop & Shop Wrap:
medium color change –
80% browning
40% browning
20% browning
30% browning
Observations: Both these tests seemed to agree that the polymer that best prevents
evaporation, being the least permeable to air or oxygen, keeps food “freshest”. We measured
water loss by observing it trapped in a bowl covered with each brand of plastic wrap. We
measured freshness as best we could by comparing the color and shape change of sliced
apples. Ideally, both these tests would be conducted over a longer period of time (than the one
day we allowed) in order to be able to measure change with instruments. We were limited to
visual, subjective observation for both tests.
CALCULATIONS & RESULTS: (Quantitative)
Test #1: Strength: How strong is the plastic wrap? How many 28 g metal washers can it hold
on its surface until it rips?
Best: Stop & Shop (at 716 washers)
2nd Best: Saran was within 2 washers (at 714)
Least Best: Glad (at 612 washers)
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300
250
200
GLAD
150
SARAN
S&S
100
50
0
Trial #1
Trial #2
Trial #3
Test #2: Stickability: How well does the plastic wrap adhere to the 3 different surfaces of
glass, paper, and plastic?
Best: Stop & Shop
2nd Best: Saran
Least Best: Glad
Note: None of the three brands adhered to paper.
SARAN: “Stuck” in 5/9 tests
Container Material
glass
paper
plastic
Holds: ¼ cup
yes
no
yes
Holds: ½ cup
yes
no
yes
Holds: 1 cup
yes
no
no
Holds: ½ cup
yes
Holds: 1 cup
yes
Glad Wrap: “Stuck” in 3/9 tests
Container Material
glass
Holds: ¼ cup
yes
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paper
plastic
no
no
no
no
no
no
Holds: ½ cup
yes
no
yes
Holds: 1 cup
yes
no
yes
Stop & Shop: “Stuck” in 6/9 tests
Container Material
glass
paper
plastic
Holds: ¼ cup
yes
no
yes
Test # 3: Permeability:
(3a) How well does the plastic wrap trap water vapor.
Best: Stop & Shop
2nd Best: Glad
Least Best: Saran
Change in water level:
Discernible change
Very slight change
No change
##1
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Heavy water
beading on
inside top &
sides
Saran Wrap (3 trials)
Light water
beading on
inside top &
sides
Glad Wrap (3 trials)
No water
seen on
inside top or
on sides
Stop & Shop (3 trials)
(3b) How well does it keep food “fresh”, keep moisture in and prevent apple from turning
brown? Results checked after 1 day, based on amount of browning.
Best: Glad
2nd Best: Stop & Shop
Least Best: Saran
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AMOUNT OF BROWNING
Glad
Saran
Stop & Shop
CONCLUSION:
According to our investigations, we give the overall “Best Buy” Designation to Stop & Shop’s
generic plastic wrap, which scored highest in three of the four testing situations. This was in
direct variance with what my daughter and I had predicted. We had thought that the cheapest,
least known brand would not be out performed in any test by the two better known plastic
wrap brands.
Saran and Glad would be a tie for my 2nd and 3rd choice, based on their strengths in different
areas. For example, Saran did well in both the strength and stickiness categories –two
important factors in preparing and storing food. Before Saran changed it formulation from
PVDC to the cheaper, “safer” LDPE, it was considered the top performer in these two areas.
Glad, invented and produced to rival Saran in the United States, has always been made of
Polyethylene, which is good at locking in moisture and flavor, safe as far as reheating and
general food safety, but not rated highest in clinginess. We predicted and were correct that this
brand would not be the best in the clinginess test but it did surpassed the other two in keeping
food (apple slices) fresh.
In short, Stop & Shop Plastic Wrap did best because it is closer to the old formulation of PVC
wrap, which had always been considered the strongest and clingiest of wraps. Whether it is the
safest for microwave reheating, as a result of the many plasticizers added, is not known to us at
this time –something to research…
I will buy Stop & Shop (a good deal for the price). The following data summarizes the tests and
results:
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Test #1: Strength
Saran: 714**
Glad:
612*
Stop & Shop: 716 ***
Test #2: Stickability
Saran: 5/9 **
Glad: 3/9*
Stop & Shop: 6/9***
Test # 3: Permeability:
3a) Trap water vapor
Saran: *
Glad: **
Stop & Shop: ***
Price Notes:
Saran Wrap: $2.89
Glad: $2.49
Stop & Shop: $1.89
:
(3b) Keep food fresh
Saran: 46% browning*
Glad: 16% browning***
Stop & Shop: 33% browning**
*** best
** second
* third
Additional Experiments That Could Have Been Done
We found it difficult to quantify “freshness” with a real-world test (how brown was the apple?).
According to the Cook’s Country website, a more scientific approach would be to purchase a
bottle of Indicating Drierite (calcium sulfate), an absorbent used in packaging which turns from
purple-blue to bright pink when exposed to moisture. Placing Drierite in bowls covered tightly
with a sheet of each wrap, the change in color of the absorbent indicates which wraps were
impermeable.
Standards:
CT Frameworks: Grades 6-8 Core Scientific Inquiry, Literacy and Numeracy
How is scientific knowledge created and communicated?
Scientific Inquiry is a thoughtful and coordinated attempt to search out, describe, explain and
predict natural phenomena. It progresses through a continuous process of questioning, data
collection, analysis and interpretation. It requires the sharing of findings and ideas for critical
review by colleagues and other scientists.
C INQ.1
Identify questions that can be answered through scientific investigation.
C INQ.2
Read, interpret and examine the credibility of scientific claims in different
sources of information.
C INQ.3
Design and conduct appropriate types of scientific investigations to answer
different questions.
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C INQ.4
Identify independent and dependent variable, and those variable that are kept
constant, when designing an experiment.
C INQ.5
Use appropriate tools/techniques to make observations and gather data.
C INQ.6
Use mathematical operations to analyze and interpret data.
C INQ. 7
Identify and present relationships between variables in appropriate graphs.
C INQ.8
Draw conclusions and identify sources of error.
C INQ.9
Provide explanations to investigated problems/questions.
C INQ.10
Communicate about science in different formats, using relevant science
vocabulary, supporting evidence and clear logic.
Processes of Science Involved:
a) Generally, there are 5 stages in an inquiry learning unit such as the “Best Buy” Testing
described above:





Engagement: stimulate students’ interest, curiosity and preconceptions;
Exploration: first-hand experiences with concepts without direct instruction;
Explanation: students’ explanations followed by introduction of formal terms and
clarifications;
Elaboration: applying knowledge to solve a problem. Students frequently develop and
complete their own well-designed investigations;
Evaluation: students and teachers reflect on change in conceptual understanding and
identify ideas still “under development”.
b) Specific processes include: observation; making predictions; controlled inquiry processes;
data collection; analysis of data; articulation of data; and drawing conclusions.
Resources:
www.metric-conversions.org.htm
www.answers.com/topic/plastic-wrap
www.edusite.com/science/products.htm
www.cookscountry.com
www.m.cooksillustrated.com
http://www.education.com/science-fair/article/determine-type-polymer-food-wrap/
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www.wiley.com “Relationship between kinds of plastic wraps and food dehydration.” Author: Janice
VanCleave
www.sciencebuddies.org/science-fair-projects/project_ideas
Gait, A. J. and E. G. Hancock. Plastics and Synthetic Rubbers. Pergamon Press, 1970.
“Keeping Food Fresh.” Consumer Reports, March 1994, pp. 143-47.
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