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Outside Magazine, February 2005

Q) Is human hair a good insulator?

A) A material's ability to keep you warm is a function of how much air it can trap. The trapped air, not the fiber itself, does the insulating. According to Yash Kamath, a materials scientist at TRI/Princeton, a New Jersey–based textile-research institute, the more crimped a fiber is, the more open structure it has for holding air. Wool, for example, is far more twisty than human hair—even a Rastafarian's—so although both fibers are made of the protein keratin, a wool hat will keep heat in far better than any head of hair. But before you start rethinking your hat inventory, be advised that the oft-cited claim that you lose most of your heat through your head is a myth. In fact, only 10 percent of your heat leaks out via the noggin, says Daniel Sessler, an anesthesiologist at the University of Louisville School of Medicine. It was a faulty 1950s study, coupled with the head's sensitivity to cold, that gave rise to the belief. A hat is a smart choice, but it's no more crucial than any other skin-covering item.

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