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Blustery winds whirl around the explorers as they pitch their tents. They've just finished ten hours of sweat-producing activity--skiing and dog sledding in frigid Arctic conditions. But these people stay warm and dry, thanks to specially designed clothing and high-tech fibers. To decide which synthetic fabrics to wear, explorers need to decide what they want their protective clothing to do. If they want it to repel water but still "breathe," they might choose fibers such as nylon or polyester or waterproof, breathable laminates and coatings. Many fabrics contain a combination of fibers. For example, if your jacket has hydrophilic (water-loving) fibers on the outside and hydrophobic (water-fearing) fibers near your skin, the inner fibers will push moisture away from your skin while the next layer of fibers will pull the moisture outward. Keeping dry is as important as keeping warm when it comes to survival and comfort in the Arctic. An adult normally loses about one liter of water a day through evaporation from the skin and lungs. During a day of strenuous activity, a person can lose ten liters of water. As the body burns energy during physical exertion, it creates heat. It then produces sweat, which provides a cooling effect as it evaporates. A sweaty person in wet clothes can lose heat rapidly if inactive in frigid temperatures. Each member of Will Steger's team will wear five layers of clothing that provide insulation. Explorers can peel off or put on layers as weather conditions and activity levels change. The first layer consists of long underwear made of a lightweight, synthetic material that allows perspiration to move away from the skin to the second layer, a synthetic fleece shirt and pants. As it wicks moisture away, the quick-drying fleece helps the underwear layer provide warmth. Next, a jacket covers the first two layers, offering insulation. Made of a heavier fleece designed for use in extreme cold, the jacket has two-way underarm zippers (as do garments in the top two layers) to help the explorer regulate body temperature. The fourth layer, a lightweight second jacket made of very fine, tightly woven microfibers, slows the rate of moisture loss. The final layer--a durable storm shell that is waterproof and breathable--protects against wind, rain, and snow. The shell is laminated with a film containing microscopic pores that allow water vapor (sweat) to escape while keeping moisture out. Team members also wear mukluks, flexible boots designed by the Inuit people and made of animal hides and canvas. Sled dogs, too, wear booties as protection from rough ice and snow. What fabrics do you normally wear? Which are the warmest and which keep you cool? Do some fabrics allow more air movement than others? What difference does a hat make in regulating body temperature? Do you notice a difference when you take off a hat you've worn for several minutes?