Evaporation Envy

    Kids, when you’re ready to play your favorite sport do you consider what you’re wearing?   Cotton clothes get wet, sticky, and heavy because they hold onto sweat.   New high-tech fabrics are different – they pull moisture away from you and through the fabric where it evaporates quickly – and cool you off.   Here you’ll compare evaporation rates for cotton and a paper towel as the stand-in for a high-tech material.

    Please note:  All chemicals and experiments can entail an element of risk, and no experiments should be performed without proper adult supervision.

    Cut two pieces each of 3” x 3” brown paper towels and cotton fabric swatches. Fill a small glass half-full with water. Mark two quart-size Ziploc bags as “room temp water” and two others as “hot water”. Add 1 cup of room temp and hot water to each appropriate bag (have an adult partner handle the hot water). Get as much air out as possible then zip closed and lay flat.

    Use an eyedropper to squirt one drop of water from the glass on the center of each towel and fabric square. Try to do this quickly so that they each get their drop at about the same time. Let the drops spread for about 15 seconds until they stop spreading. Place one towel and one fabric swatch each on top of the “room temp” and “hot water” baggies. Observe every three minutes and compare the amount of water on each spot. Record your results. What do you observe? The paper towel should have much larger pores than the cotton fabric, and it behaves like the high-tech fabrics would in this test.

    Where’s the chemistry? High-tech fabrics in modern sports clothes have pores to move water away from the skin and to the outer surface of the fabric. These pores provide a way for sweat to evaporate faster, keeping you dry and comfortable. Evaporation happens when water is heated and goes into the air. It takes energy to evaporate water. Heat is a form of energy, and water evaporates more quickly at warmer temperatures. Materials that soak up water (like cotton) hold onto it longer due to a slower evaporation rate. Materials with pores allow faster evaporation, like those used in high-tech clothing. Check out triathlon suits (“trisuits”) as just one example.


    Kathleen Carrado Gregar, PhD, Argonne National Labs 
    [email protected]
    October 2008



    National Chemistry Week is October 19-25, 2008. The theme this year is “Having a Ball With Chemistry” and is all about the chemistry of sports. The American Chemical Society has published a newspaper called “Celebrating Chemistry” for National Chemistry Week that contains several activities, one of which is called “Evaporation Exploration” and used for this article. The editor is Judith Jankowski. See, click on Education, and look for the Community Outreach section. Or inquire at ACS, 1155 16th St. NW, Washington, DC 20036.