Wednesday, September 28, 2016

Cooler Fabrics

Staying warm indoors is easy; just put on a sweater, sweatshirt, or light jacket. But staying cool under warm conditions indoors has its limits. It's generally not socially acceptable to take off all clothing or even strip down to just a cotton t-shirt in a hot office. But soon there may be a solution. By taking advantage of knowledge of how the human body cools itself, researchers at Stanford University believe that they have developed a clothing fabric that can keep the wearer significantly cooler than other fabrics such as cotton. Their findings are documented in the Sept. 2 issue of Science and explained in layperson's terms in Forbes Magazine.

Except when a person is sweating, the body loses most of its heat as radiant heat energy in the infrared part of the wavelength spectrum. (You can't see infrared radiation because its wavelength is longer than visible light.) The problem is that fabrics such as cotton reflect most of this radiant heat back toward the body; that's partly how they keep the body warm. Understanding this, the researchers started with sheets of opaque polyethylene that allow 90% of IR radiation to pass through (cotton only transmits 5%.) Then they punctured it with tiny needles to allow air to pass through and added a substance that allows the fabric to wick moisture away. Finally, to make the material feel more like traditional fabrics they bonded two sheets of the material to a middle layer of widely spaced cotton mesh.

Then they tested the new fabric. In a room kept at 23.5oC the temperature of bare skin was 33.5oC, skin covered with cotton was 37oC, and skin covered with the new fabric was 35oC. That's fully 2oC lower than cotton, giving the new fabric an advantage in a warm room.

There's no guarantee that the new fabric will catch on with clothing designers. But at least it introduces a new way of thinking about how to create new fabrics for specific purposes, based on human physiology.

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