This may be a bit basic for folks, but I see tons of people getting it wrong, so I thought I’d write this up.
Layers are the key to keeping warm and dry. When we talk about layers, quality and type are MUCH more important than quantity of layers. More clothes is never the right answer unless you’re wearing the right KIND of clothes.
There are three kinds of layers: wicking, loft (insulation) and wind breaking.
Wicking layers transfer moisture away from your skin. They’re responsible for keeping you dry. They offer a bit of insulation too, but that is not their primary purpose. These are the first layers that you put on.
They can be as simple as an inexpensive base layer or synthetic long-underwear or as complex as high tech base layer where different zones of your body are covered with different thicknesses and textures of fabric to maximize warmth and moisture transfer. Wicking layers can be as cheap as a $8 technical t-shirt from Walmart or as expensive as $150 base layer.
Wicking layers can be used anywhere on your body. They exist for gloves, shirts, tights, socks and even hats.
For my core, I’ve had very good luck with inexpensive base layers made by a company called Verge. They can be found for as little as $8 for sleeveless tops. Like anything synthetic, they tend to trap odors after a while. At $8 each, it doesn’t hurt to recycle them after a year.
My favorite for this time of year are made of merino wool. They’re soft, warm and have a very wide temperature range. They cost $40-80 each and are made by a variety of manufacturers.
COTTON IS NEVER A GOOD WICKING LAYER! Cotton traps moisture and holds it. Once your body warms up, you'll start to sweat, then you'll freeze.
Loft or insulating layers provide insulation. They create dead air space between your outer layers and wicking layers. Moisture must transmit through, but their primary source is to hold your body heat in. Winter jerseys often have a little fleece on the inside to provide loft. Microfleece can work well for this. Some jackets (soft shells) have fleece in them too to add loft.
COTTON IS NEVER A GOOD INSULATING LAYER! Like I said above, it traps moisture and holds it. You warm up fast and then freeze fast.
Wind Breaking layers are meant to keep wind and wet out while allowing perspiration to leave. Seems simple, eh? It isn’t. If they don’t breathe well enough, it is very easy to overheat, sweat and soak yourself… thus causing a serious danger of freezing. Most simply, vents are holes in high temp areas under your arms or on your back to let sweat and some heat out. More complex venting can be done using fancy laminated fabrics that keep moisture out, but let your skin breathe. Gore-Tex is the one that comes to mind most readily, but there are many other fabrics on the market that do this. The best jackets, vests, pants, gloves use a combination of high tech fabrics and simple venting to balance keeping warmth in and getting/keeping moisture out.
Wind breaking layers can be as inexpensive as a simple nylon windbreaker or can cost hundreds and hundreds of dollars. Same with tights, pants and gloves.
You’ll notice I have been talking most about keeping my core (torso) warm. While the layers really apply to most places on the body, the key part that I concentrate on is keeping my core at the right temperature.
Combination Layers: There are wicking layers that have insulation. There are insulating layers with wind/water breaking panels. There are wicking layers with wind breaking layers. I use them from time to time.