Visualize Microcapsules that keep you comfy.
By Tracy Staedter
Winter presents an interesting apparel challenge for those who want to play outside. Wear too many
layers and youÕll sweat; wear too little and you'll freeze your fanny. Lately, technology has offered
up a solution: a paraffin-wax-like substance known as phase change material encapsulated
in microscopic balls of heat-resistant plastic similar to that used in dishwasher-safe dinnerware.
Coated onto fabrics, the phase change material melts and freezes before you do and, in the process,
stores and expels heat energy. Clothing can now be engineered to respond to your body
temperature--and heat up or cool down to keep you feeling just right.
Phase change materials work because they are designed to maintain the midpoint of a narrow
temperature range. One phase change material used in fleece jackets, for example, stays between about
27 °C and 38 °C when worn--or around 32 °C, which feels comfortable next to the skin. The specific
range is determined by the lengths of the hydrocarbon molecules that make up the material;
in different proportions they specify different ranges.
When a skier puts on the jacket, some of the phase change particles absorb body warmth and partially
melt. During a strenuous run down the mountain, the skierÕs body generates excess heat, which melts
the remaining microcapsules. Because the heat is absorbed by the melting material rather than
reflected back toward the body, the temperature inside the garment stays comfortable. On the
chairlift ride back up the mountain, the skier cools down. But as the temperature between the
jacket and the body drops, the microcapsules refreeze--in the process releasing their stored heat.
The phase change material can run through these thermal cycles indefinitely, easily outlasting the
life expectancy of the garment.
Two companies specialize in this material: Frisby Technologies in Winston-Salem, NC, and Outlast
Technologies in Boulder, CO. By early 2003, just about every major brand of outdoor apparel will
offer a line of clothing made with phase change materials, turning more fair-weather fans toward
cold winter fun.
Technology Review.
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