Hands-on Activity: What Is the Best Insulator: Air, Styrofoam, Foil or Cotton?

Contributed by: Center for Engineering Educational Outreach, Tufts University

Photo shows a family of six people having a picnic in a park. They are sitting at a picnic table with a cooler and thermos nearby.
Ice coolers work as insulators to keep drinks and food cold so that family picnics can be enjoyed
Copyright © U.S. Department of Agriculture http://snap.nal.usda.gov/family-having-picnic-park


That heat flows from hot to cold is an unavoidable truth of life. People have put a lot of effort into stopping this natural physical behavior, however all they have been able to do is slow the process. Student teams investigate the properties of insulators in their attempts to keep cups of water from freezing, and once frozen, to keep them from melting.

Engineering Connection

Temperature regulation is important in many aspects of engineering. Packaging engineers design containers and systems to be able to reliably ship items at specific temperatures. Mechanical engineers make sure that working engines do not overheat, and electrical and computer engineers design electronics so that they do not overheat. Civil engineers specify the most suitable insulating materials for the climates where their structures reside. Temperature regulation applies an understanding of the principles of heat transfer, which is relevant in almost all engineering disciplines.

Learning Objectives

After this activity, students should be able to:

  • Explain what "insulate" means and its implications in keeping things cold or warm.
  • Conduct basic experimental processes.
  • Describe how natural materials differ from human-made materials in terms of insulation.

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  • Make observations to provide evidence that energy can be transferred from place to place by sound, light, heat, and electric currents. (Grade 4) Details... View more aligned curriculum... Do you agree with this alignment?
  • Tell and write time to the nearest minute and measure time intervals in minutes. Solve word problems involving addition and subtraction of time intervals in minutes, e.g., by representing the problem on a number line diagram. (Grade 3) Details... View more aligned curriculum... Do you agree with this alignment?
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  • Things that are found in nature differ from things that are human-made in how they are produced and used. (Grades 3 - 5) Details... View more aligned curriculum... Do you agree with this alignment?
  • Materials have many different properties. (Grades 3 - 5) Details... View more aligned curriculum... Do you agree with this alignment?
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  • Describe how water can be changed from one state to another by adding or taking away heat. (Grades 3 - 5) Details... View more aligned curriculum... Do you agree with this alignment?
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Materials List

Each group needs:

  • 4 3 oz. plastic cups
  • 4 larger clear plastic cups
  • 3 Styrofoam cups
  • aluminum foil, 8½-in x 11-in piece
  • 20 cotton balls
  • teaspoon-sized spoon
  • 4 rubber bands
  • Data Chart, one per student, to be filled in during the experiment
  • Results Chart, one per student, to be filled in after the experiment

To share with the entire class:

  • pitcher of warm water
  • plastic wrap
  • baking pan
  • large book or magazine
  • freezer


Photo looking into an open plastic cooler filled with ice, beverages, sandwiches, fruits and vegetables.
Copyright © U.S. Department of Veterans Affairs http://www.milwaukee.va.gov/articles/dietician1.asp

When you go to a summer picnic at a beach, in the mountains or at a lake, why do you put your cold drinks and ice in a cooler? What would happen if you put them in a backpack instead? (Listen to student ideas.) Yes, that's right, you would end up with a wet backpack and warm drinks. The cooler helps to keep the drinks cold because it acts as an insulator and slows the transfer of energy from one source to another, meaning it helps keeps the inside of the cooler cold and the heat out.

The opposite of an insulator is a conductor. What do you think a conductor does? (Listen to student ideas.) Yes, that's right, a conductor speeds up the transfer of energy from one source to another. You may have experienced this if you ever removed the lid to a pot cooking on the stove. A metal pot is a conductor and heats up quickly on the stove so that it cooks food or boils water faster. Just be careful before touching a metal pot because you could get burned.

What would happen if you designed a cooler using a material that acts as a conductor? Or a cooking pot with a material that acts as an insulator? (Listen to student ideas.)


conductor: A substance or body that can allow electricity, heat or sound to pass through it.

conservation of energy: A physics principle that states that energy can neither be created nor destroyed and that the total energy of a system by itself remains constant.

energy: The capacity for doing work; can be in many forms such as electrical, mechanical, chemical, sound, light and heat.

freeze: The process of changing from a liquid to a solid (as ice) by loss of heat.

heat: A form of energy that causes substances to rise in temperature or go through associated changes (melting, evaporation or expansion).

insulate: To prevent or slow the transfer of electricity, heat or sound from one environment to another.

insulator: A substance that resists the flow of heat, electricity or sound through it.

melt: The process of changing from a solid to a liquid state through heat gain.



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. Plastics and rubber are usually good insulators. It is for this reason that electrical wires are coated 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 for this reason.

Before the Activity

  • Gather materials and make copies of the Data Chart and Results Chart, one each per student.
  • To minimize the time spent in the classroom, prepare the insulating materials (although students CAN do this!!).
  • Break up the foam cups into small pieces.
  • Tear the aluminum foil into pieces and loosely crunch up the pieces.
  • Pull the cotton balls apart a little and flatten them so that they resemble pancakes.

With the Students

  1. Present the Introduction/Motivation content. As a class, discuss what types of devices students have seen or used to keep things warm or cold. Talk about the materials from which they think these devices are made.
  2. Divide the class into groups of two to four students each.
  3. Have students examine the insulating materials they are going to be given and have groups make predictions about which they think will work best.
  4. Hand out the materials and blank charts to each group.
  5. Give each team its supply of three different insulating materials: Styrofoam, aluminum foil and cotton balls. Air is the fourth insulating material. Have students place enough of each insulating material in each large plastic cup so that it covers the bottom of the cup. Put nothing in the fourth large cup because air will serve as the insulator for that cup.
  6. Place a small 3 oz. cup in the center of each large cup.
  7. Have students fill the space between the cups with the same insulating material they used on the bottom.
  8. Place 3 teaspoons of warm tap water in each small cup.
  9. Have each group cover each of its large cups with plastic wrap held on by a rubber band.
  10. Place the cups in the freezer. Check the cups every 15 minutes to see which cup forms ice first. Record observations in the data chart. Keep checking until you see ice form in all four cups.
  11. Let the cups sit in the freezer until the ice is frozen solid in all cups.
  12. Remove the cups from the freezer and place them in a baking pan.
  13. Place a book or a magazine on top of the cups to keep them from tipping or floating.
  14. Pour very warm tap water into the pan.
  15. Have teams check their cups every few minutes to see which seems to be melting first, second, third and fourth. Record observations in the data chart.
  16. Conclude with a class discussion to share and compare results and findings. Ask the Investigating Questions. Use the attached rubric to gauge student accomplishments.


Investigating Questions

  • 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? Explain.
  • Which is best for insulating a cup of ice: Styrofoam, foil or cotton?


Pre-Activity Prediction: Have students feel and examine the test insulating materials (Styrofoam, aluminum foil, cotton, air), and have groups make predictions about which they think will work best. Their predictions give some indication of their understanding of heat transfer and insulation concepts.

Embedded Assessment: Observe students during the experimental process. Evaluate their comprehension of the subject matter and activity engagement using the criteria provided in the Rubric for Performance Assessment, which considers their understanding of insulating materials and teamwork.

Homework: Ask students to write paragraph-long answers to the two following questions, to turn in the next day or share in a class discussion. Review their answers to gauge their comprehension of the activity content.

  • Would you rather have gloves made of fabric or aluminum foil? Explain your choice using what you know about the properties of heat transfer. (Example answer: Fabric gloves would keep my hands warmer than foil gloves because fabric insulates our bodies, slowing down the time it takes for our hands to become cold. On the other hand, metals speed up the transfer of heat so any warmth in my hands prior to putting on "aluminum gloves" would quickly escape through the foil, leaving me with very cold hands.)
  • List at least three different products, devices or structures for which engineers applied their understanding of heat transfer principles in designing systems or choosing materials for the purpose of temperature regulation. (Tip: Think what might be designed by packaging, mechanical, electrical, computer and civil engineers, maybe items you use every day for comfort, life-saving necessity and entertainment.) (Example answers: thermos beverage containers, ice cream cart coolers, refrigerated trucks to ship foods at specific temperatures, coolers used to store and transport donated blood and body parts to patients, insulating materials in house walls and roofs to keep the inside cool or warm, special materials and weaves of fabrics used for clothing designed for specific weather conditions, wires made of metal and coated in plastic, fans and the liquids in radiators to keep electronics and motors from overheating. Specific example: If the casing that surrounds a tablet computer or pocket computer was made of rubber, the device would become hot very fast, and too uncomfortable to hold.)

Graphing: Have each student create a bar graph of the time taken to freeze/melt water for each insulator used. Use data obtained from the Data Chart for the bar graph.

Activity Extensions

So students can experience first hand that foil is not a good insulator, extend the activity with this quick hands-on demonstration:

  • Have each student wrap a cup with aluminum foil and another cup with paper.
  • Pour ice water into the cups.
  • Have students hold the cups in their hands to judge which material is the best insulator.


Kessler, James H. and Andrea Bennett. The Best of WonderScience: Elementary Science Activities. Boston, MA: Delmar Publishers, 1997. pp 207, 210-211. ISBN: 0827380941


© 2013 by Regents of the University of Colorado; original © 2004 Worcester Polytechnic Institute

Supporting Program

Center for Engineering Educational Outreach, Tufts University


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Last modified: April 26, 2017