Here's a brief description of the three layers:
* FOUNDATION - The purpose is to ``wick'' or draw moisture away from the body without the garment absorbing it. Cotton gets soaked; wool and silk also retain moisture. Newer synthetic materials range from polypropylene to high-tech polyester. Brand names include Patagonia's Capilene, DuPont's Thermax, and Terramar's Transport.
* INSULATION - To keep body heat in without too much bulk or trapping of body moisture. Older materials: down, wool, polyfill. New: high-tech polyester. Familiar names include DuPont's Quallofill, Thermolite, and Thermoloft; 3M's Thinsulate.
Microfiber polyester fleeces are especially popular (sometimes made from the fiber reclaimed from recycled plastic soft-drink bottles). Names include: Malden Mills's Polartec; Helly Hansen's Propile, and Dyersburg's Dyersport (made from Wellman Inc.'s Ecospun).
* OUTER SHELL - To protect from the elements, such as wind, precipitation, and cold. Most outer shells include different combinations of synthetic materials such as polyester, polyurethane, and nylon.
Microfibers, made from ultra-fine polyester yarns (less than the size of a human hair) densely woven for high level of water repellancy are often soft, but may not be as waterproof as some other materials. Brand names include DuPont's Supplex, Wellman's Fortrel Microspun, Burlington's Versatech.
Waterproof breathables incorporate a laminating process, usually on one side of a fabric. The resulting membrane - or micro-pores - keeps water droplets out, while allowing the fabric to ``breathe'' (so that vapors can pass through). Brand names include Gore-Tex, Patagonia's H2NO lines, Burlington's Ultrex, and AZKO's Sympatex.