**Layer 1 **
**Moisture Control **
When your muscles generate chemical heat in excess of what your body needs to remain comfortable, you sweat. This creates evaporative cooling, which is good when you're half-naked at the beach but troublesome when you're wearing a parka on a snowy deer stand. In addition to sucking heat from your body at a rate 25 times faster than air, water (perspiration in this case) fills the dead-air spaces in your clothing, drastically reducing the fabric's ability to insulate. To avoid sweat soaking into and freezing in your base layer, you have two options. You can wear wool, which retains body warmth even when wet, or you can wear one of the synthetic fabrics that don't absorb water, such as polyester, olefin (polypropylene) or nylon. While each of these man-made fibers repels water, wicking rates vary slightly depending on how the fabrics are woven, brushed or treated. Patagonia's Capilene, for instance, is polyester treated with a chemical that increases moisture transfer away from the skin. Similarly, Cabela's MTP Tech-Silk is a polyester treated with a chemical trade-named Visa, which reportedly increases wicking.