Most of us have had the experience of grabbing a pair of damp jeans from the dryer and pulling them on (with difficulty) because we were late for something. Think back carefully about the cold clammy feeling of that damp denim on your legs. And remember how long it took for them to dry? Probably several hours, right? I've said it before and I'll say it again: cotton is a terrible clothing choice for cool and damp conditions. Cotton fibers hold water much longer than synthetic or wool fibers, and this allows damp cotton clothing to steal precious body heat when you’re wearing it next to your skin. Of course, layering helps—but even good fabric isn’t much help when worn over or underneath a damp cotton layer. The moral of this story is simple, if it’s cold enough for long johns, they shouldn’t be cotton. In fact, none of your clothing should be cotton in those conditions. From your socks to your hat, and everything in between, choose synthetic fabrics or the perennial outdoor fabric: wool.