Activity: What is the Best Insulator: Air, Styrofoam, Foil, or Cotton?



Heat flows from hot to cold an unfortunate truth of life, people have put a lot of effort into stopping this fact, however all have been able to do is slow the process. Working in groups of three to four, the students will investigate the properties of insulators in attempts to keep a cup of water from freezing, and once it is frozen, to keep it from melting.

LEVEL OF DIFFICULTY [1 = Least Difficult : 5 = Most Difficult]



20 minutes to set-up
2 ½ hours to freeze
1 ½ hours to melt


$1.00 per group


1.1 Identify materials used to accomplish a design task based on a specific property (i.e., weight, strength, hardness, and flexibility).
2.1 Identify a problem that reflects the need for shelter, storage, or convenience.

What "insulate" means and its implications in keeping things cold/warm
Basic experimental processes
How natural materials differ from human-made materials in terms of insulation

INSULATE: to prevent or slow the transfer of electricity, heat, or sound from one environment to another
CONDUCTOR: a substance or body that can allow electricity, heat, or sound to pass through it
NONCONDUCTOR: a substance that resists the flow of heat, electricity, or sound thruogh it.
HEAT: a form of energy that causes substances to rise in temperature or to go through associated changes (as melting, evaporation, or expansion)
ENERGY: the capacity for doing work, energy can be in many forms such as electrical, mechanical, chemical and solar.
CONSERVATION OF ENERGY: a principle in physics that states that energy can neither be created nor destroyed and that the total energy of a system by itself remains constant
MELT: the process of changing from a solid to a liquid state through heat gain
FREEZE: the process of changing from a liquid to a solid (as ice) by loss of heat

Insulation helps keep cold things from warming up and warm things from cooling down. Insulators do this by slowing down the loss of heat from warm things and the gaining of heat by cool things. Usually plastics and rubbers are good insulators. It is for this reason that they coat electrical wires to make them more safe to handle. Metals, on the other hand, usually make good conductors. In fact, copper is used in most electrical wires and circuit boards.
RESOURCES: - phase changes and phase diagram - phase changes - Energy description

4-3 oz. plastic cups per group
4-larger clear plastic cups per group
Warm water in a pitcher
Insulating materials (3-foam cups per group, 1- 8 ½" x 11" piece of aluminum foil per group, 20 cotton balls per group)
4-Rubber bands per group
Plastic wrap
Baking Pan
Large book or magazine

Obtain the materials
To minimize the time spent on the activity in the classroom, you can prepare the insulating materials (though students CAN do this!!):
Break up the foam cup into small pieces
Tear the aluminum foil into pieces and loosely crunch the pieces up
Pull the cotton balls apart a little and flatten them so that they resemble pancakes


Discus with your students what types of devices they have seen or used to keep things both warm or cold. Talk about the materials they think these devices are made out of. Have the students examine the insulators they are going to be given and have the groups make predictions about which will work best.
1. Have the students work in groups of two or three.
2. Give each group the materials they will need.
3. Each group will have four different insulators: air, styrofoam, aluminum foil, and cotton balls. Have the students place enough of each insulating material in each large plastic cup so that it covers the bottom of the cup. Do not put anything in one of the large cups because the air will be the insulator for that cup.
4. Place a small 3 oz. cup in the center of each large cup.
5. Have the students fill the space between the cups with the same insulating material they put on the bottom.
6. Place 3 teaspoons of warm tap water in each small cup.
7. Have each group cover all of their large cups with plastic wrap held on by a rubber band.
8. Place the cups in the freezer. Check the cups every 15 minutes to see which cup forms ice first. Keep checking until you see ice form in all four cups, and record observations on chart provided (see link).
9. Allow the cups to sit in the freezer until the ice is frozen solid in all of the cups.
10. Take the cups out of the freezer and place in a baking pan.
11. Place a book or a magazine on top of the cups to keep them from tipping or floating.
12. Pour very warm tap water into the pan.
13. Have the class check their cups every few minutes to see which one seems to be melting first, second, third, and fourth.

For students to experience first hand that foil is not a good insulator, you can follow up the activity with this suggestion:
1. Have students wrap a cup with aluminum foil and another cup with paper.
2. Pour ice water into the cups.
3. Have the students hold the cups in their hands to judge which material is the best insulator.

What does "insulate" mean?
What materials are used for insulation?
Which insulator was best at slowing down the loss of heat from the warm water? Which was the worst?
Did the results in the second half of the activity make sense with the results from the first half?
Is Styrofoam, foil, or cotton better for insulating a cup of ice?

Kessler, James H. and Andrea Bennett. The Best of WonderScience: elementary science activities. Boston: Delmar Publishers, 1997. p 207, 210-211 ISBN: 0827380941*

*Adapted with permission from The Best of Wonderscience, Copyright 1997, American Chemical Society Published by Wadsworth Publishing, Inc.. If you enjoyed this activity check out, Your Science Place in Cyberspace, for free elementary physical science activities.


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See Associated Download.