PURPOSE:  To compare the effectiveness of winter clothing materials for retaining heat.

MATERIALS (per group of four students):  4 identical plastic one-liter soft drink bottles, one square of unwashed cotton denim, one square of heavy weight cotton flannel or heavyweight cotton corduroy and one square of wool flannel to cover containers, 4 thermometers, cardboard fan, clock with a second hand, spray bottle, tape; large container of hot water (about 80^oC) for class.

INTRODUCTION: Hypothermia, significant cooling of the body core, is a potential complication of outdoor activities, especially in the winter. Proper clothing protects the body by conserving heat. Air is an excellent insulator, and a layer of trapped air next to the skin is essential for maximum heat conservation. Water is not as good an insulator as air and can drain heat away from the body. Evaporation of the water near the skin cools extremely effectively. Proper clothing fabrics will hoald air, not water, agains the skin. The more air that is trapped, the more effective the clothing will be in conserving heat. The weave of the fabric, or the type of knit will be as important as the fiber used. In this experiment you will compare two different weaves of cotton -- napped, and unnapped -- and a napped wool. Napped fabrics are those in which fibers are combed to be perpendicular to the thread. Each will be compared wet and dry. The comparative effectiveness of the fabric will be determined by the drop in temperature of the water over time. 

In this activity, you will compare the effectiveness of clothing fabrics for retaining heat in a warm body.  The "warm bodies" will be containers filled with hot water. The "clothing" will be cotton and wool fabric fitted over the containers. The comparative effectiveness of the fabric will be determined by the drop in temperature over time in the containers.  You will test the effectiveness of both fabrics under dry and wet conditions.

PREDICTIONS:

1.  Will the containers differ in the rate of cooling under dry conditions?  If so, how?  Explain your ideas.

2.  Which container will lose the most heat when wet?  Explain your ideas.

PROCEDURE:

A.  Fill all 4 containers to the same level (about 3/4 full) of hot water from the class container.  If necessary dry the outside. Carefully tape the three different fabrics around three of the containers.   DO NOT GET THE FABRIC WET.  The uncovered container will serve as the control. 

B. Take temperature readings in each container as follows:  Insert a thermometer into each container and GENTLY stir the water for about one minute without touching the sides or bottom of the container.  Record the initial temperature on the data sheet.  Then record the temperature every minute for the next 7 minutes, gently stirring the water for about 5 seconds before each reading.

C. With the spray bottle, evenly mist the cans with cool water until the fabric is ALMOST saturated.  Continue to record the temperature at one minute intervals for the next 7 minutes.

D.  Finally, use a stiff piece of cardboard to fan all three cans.  Continue to record the temperatures at one minute intervals for the next 7 minutes.

E.  Construct a graph with temperature in ^oC on the vertical axis, and time in minutes on the horizontal axis.  Plot the points on the graph for each set of data and connect the points as follows:

___ uncovered - - - wool fabric . . . cotton fabric .... denim

CONCLUSIONS:  Examine your graph to determine the effectiveness of the three different kinds of fabrics under dry, wet, and windy conditions compared to the uncovered container.

3. What was the purpose of the control (the uncovered container)?

4. Which fabric was the most effective at keeping the body warm under dry conditions?  Was your prediction correct?

5. What effect did wetting the material have on the cooling rate?

6. Which material lost more of its effectiveness when wet?  Was your prediction correct?

7. What effect did fanning the wet containers have on cooling?

DISCUSSION:

8. What does this experiment tell you about wearing blue jeans on a winter outing?

9. What other factors, besides the kind of fiber, could have affected the cooling rates of the fabric-covered cans?

10. Using what you know about dressing properly for winter weather, what changes would you suggest for the hiker pictured above to reduce the danger of hypothermia?

11. Besides appropriate clothing, what other safeguards should be taken before going out on a winter hike?

POSSIBLE NEW QUESTION:

Does the fabric or the weave have more effect on cooling? Why?

Answer: Since the trapping of air is the main objective, the weave should have a greater effect.