I've never really understood the principles of layering. For cold weather treks, should my baselayer be cotton or wool? What about my midlayer? Wool? Fleece? What are the basics of layering for any occasion?
Submitted by - Joe, from Binghamton, NY
Thanks for asking this question. It's something we often take for granted–that people know why layering is important and how it works. There are three main components to a layering system. Here's the gist:
1) Next to skin: The main job of this layer is to wick sweat away from your skin, then dry quickly so you don't get chilled. Cotton sucks at this because it takes forever to dry. My favorite base layers are wool. They are very efficient, warm when it's cold, cool when it's hot, and they don't stink up like so many synthetics do. The con is that wool tends to dry slowly when it gets wet (either from precip or sweat). Synthetic materials (polyesters) also make good base layers, and people with very sensitive skin often find wool itchy, so poly is a good wicking, quick-drying option. Perhaps the best of all are wool/synthetic blends which are becoming more and more popular because they have the quick-dry ability of synthetics, with the warmth and ant-stink talents of wool. A note about fit: For cool or cold weather, your base layer should be snug, because if it's not touching your skin, it can't wick sweat. That means your sweat sits on your skin until it evaporates, which leaves you shivering.
2) Insulation: This is the layer that traps your body heat. It can range from lightweight fleeces and wool sweaters to full-on puffy down jackets; it just depends on the season. In all but the coldest of weather, your insulation will remain in your pack while hiking, so your body heat can escape and dissipate. But as soon as you stop moving, put it on so you won't get cold as your sweat dries.
3) Shell: The job of a shell is twofold: it cuts the wind and keeps you dry. In summertime, you can get away with a wispy windshell, but for more challenging weather and extended trips, you want a waterproof/breathable shell (like Gore-Tex or eVent) that keeps water out, but lets sweat vapor escape, so you don't get wet from perspiration inside your layering system.
The guiding principle of layering is that you are regularly adding and removing layers to keep your body temperature even. An example. I start off on chilly morning hike wearing my base layer and a light fleece. As my body warms up, I stop to remove the fleece. At lunch break, on a breezy ridge, I immediately put the fleece back on, and possibly my outer shell to cut the wind. After lunch, it all comes off (except the base layer) and I start hiking. Afternoon thunderstorms roll in. I throw on my shell and open up the pit zips (underarm vents) and continue hiking. I always make sure my extra layers are conveniently located in the outer pockets of my pack, so I can always reach them. Happy trails! —KRISTIN