Hairy: How Does Hair Keep Animals Warm?

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Author: Janice VanCleave


How does hair keep animals warm?


  • Box, at least 2 inches (5 cm) taller and wider than one of the jars
  • Cotton balls
  • 2 1 quart (1 liter) jars with lids
  • 1 cup measuring cup
  • Water
  • 2 thermometers




  1. Cover the bottom of the box with a layer of cotton balls.
  2. Set one jar in the box.
  3. Fill the box with cotton up to the top of the jar.
  4. Use the measuring cup to add 2 cups (500 ml) of warm water from a faucet to each jar.
  5. Stand a thermometer in each jar of warm water for one minute.
  6. Read and record the temperature of the water in each jar.
  7. Remove the thermometers, and seal each jar with a lid.
  8. Quickly cover the jar in the box with a layer of cotton balls.
  9. Close the lid on the box.
  10. Leave the jars undisturbed for ten minutes.
  11. Uncover the jars, and stand a thermometer in each jar.
  12. Allow the thermometers to stand for one minute.
  13. Read and record the temperature of the water in each jar.


The water in the jar that was placed in a box and surrounded by cotton stayed warmer than did the water in the uncovered jar.


The cotton keeps the water in the jar warm because it prevents the heat inside the water from escaping too quickly. Much of the space around the jar in the box is filled with quiet, motionless air. The cotton balls are filled with air molecules. Heat from the warm water is conducted (transferred) to the cotton and the molecules of air trapped between the fibers of the cotton. Because the air is trapped, the heat IS not earned away from the jar as it is in the uncovered jar. Molecules of air touching the uncovered jar pick up heat energy and take it away. Hair on animals like the cotton fibers, traps air and prevents the heat produced by the body from escaping.

Let's Explore


  1. Would a different covering around the jars affect the results? Repeat the experiment, but prepare two boxes and replace the cotton with feathers obtained from a pet store in one box and use woolen yam instead of cotton in the second box. Science Fair Hint: The materials used, photographs, and diagrams along with the results from the experiments can be used as part of a project display.
  2. Does the box affect the results? Change the experiment by using a woolen and a cotton sock to cover jars containing warm water. Measure the temperature of the water before covering and at ten-minute time intervals for one hour.
  3. Does an animal's hair keep it cooler in hot weather? Repeat the experiment using cold water. Determine if hair can act as an insulator to keep animals cool during hot summer weather.

Show Time!


  1. Nature provides many examples of energy conservation. During the winter, a bird stays warm by fluffing its feathers to trap air. To stay cooler during hot weather, the feathers are squeezed against the bird's body to remove the trapped air. What other ways do animals have to keep warm or stay cool?
  2. "Goosebumps" cause individual hairs to stand on end. This keeps animals warmer because the standing hairs trap and hold a layer of still air around the body of the organism. What makes the hair stand erect, and what produces the bump the hair stands in? Use a diagram to show how "goose bumps" aid in warming the skin.

Check It Out!

The hairs on polar bears are a little like solar-heat collectors. They are hollow tubes that can trap light energy and funnel it to the skin of the bear. Find out more about the bear's hair.

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