Many winter hikers use a four-layer clothing system:
- A base layer, consisting of a synthetic wicking long-sleeved shirt and long underwear.
- A fleece sweater as an insulating mid-layer.
- A hardshell jacket and pants as a wind-proof/waterproof layer.
- A puffy down or synthetic jacket and pants for even more warmth.
During the day when you are active, you’ll most likely be wearing layers 1-3, in addition to gloves and one or more hats, although during periods of high exertion you may take off layers 3 and 2 to vent as much extra heat as possible in order to avoid sweating. If you do sweat, the function of your base layer is to move the sweat away from your skin and into layers 2 and 3 where eventually evaporate without chilling you, because it’s in a higher layer.
Generally, you really only need the 4th insulation layer when you stop for a break, for hanging around camp, or for very cold summit conditions and high windchill.
When you go to buy winter hiking layers, it’s tempting to buy a jacket that combines layers 2 and 3, the insulating layer with a windproof shell in order to save money. There are also many coats available that are waterproof hard shells with a built-in fleece liner, snowsport jackets that have added down or synthetic insulation in them, or so-called 3-in-1 component jackets which only contain 2 components, an exterior waterproof/breathable shell and inner fleece/insulated jacket that can be zipped out. While these might be suitable for downhill skiing or riding the school bus, I wouldn’t recommend them for winter hiking, backpacking, or mountaineering.
Instead, my advice is to implement each of your layers using a different best-of-breed garment. This gives you the most flexibility and lets you select garments that are optimal for a specific function. It’s also far easier to control your heat level with individual garments versus garments that combine two layers into one, and the failure of a single piece of clothing (broken zipper, for instance) will only compromise one of your layers and not potentially two.
Keep it simple: a separate garment for each layer.