In the mountains, even when it's very cold, you don't need to stack multiple layers of clothing to stay warm. Technical clothing has been developed specifically for outdoor sports lovers to give them optimum protection from the elements throughout their outdoor antics. With changing climatic conditions as well as alternating periods of effort and rest, a basic principle must be followed to stay comfortable: the three-layer system.
No more heavy wool sweaters worn over a turtleneck and a cotton undershirt, covered with a big warm jacket at the risk of ending the day wet and frozen, the now widely approved three-layer system has revolutionised the way we dress for sports. Three cleverly superimposed layers are enough to stay warm and dry all day long. Indeed, the final objective of the three-layer system is to keep you dry and warm, and to wick away moisture (from the perspiration produced during exercise).
Basically, the base layer performs the breathable function by wicking away perspiration and keeping the body "dry", te mid layer ensures a comfortable temperature through insulation, and the outer layer (sometimes called the shell, or outer shell) protects you from the elements by being water resistant and windproof. This optimal combination of different types of technical clothing will give you the perfect protection from whatever the day's conditions hold.
Worn next to the skin, this layer must be able to transfer sweat away from your body: it's whole purpose is to wick perspiration away as quickly as possible during exercise to avoid your skin feeling damp. It's important because if your skin is wet, you'll begin to feel cold. It's absolutely necessary to banish that tee-shirt or cotton turtleneck that traps moisture and causes you to feel freezing cold when you stop exercising. An effective base layer can be selected from a range of technical undergarments made of natural fibres such as merino wool, or synthetic fibres such as polyamide, polyester or lycra. Design-wise, short or long sleeves, round or zipped collar, there's plenty of options to choose from.
Worn over the technical base layer, the mid layer corresponds to a top that keeps you warm. More precisely, it has a double mission: it should insulate your body from the cold while also being breathable. This layer is available in varying degrees of warmth (different grammages), so you can choose according to the outside temperature. It's imperative that the mid layer continues to wick moisture towards exterior so as not to inhibit the work of the base layer. The fleece or similar synthetic top is very effective thanks to its insulating performance and its ability to dry quickly. Light micro-down jackets, either natural or synthetic, are also a good choice because they are very warm and compact. The mid layer must be easy to remove and store,perhaps in a backpack, to prevent overheating.
In direct contact with the elements, the outer and final layer must protect from bad weather such as rain, snow and wind. In addition to being water resistant and windproof, this layer must also be breathable to continue the wicking functionality of the two previous layers by moving moisture to the exterior shell. It can also bring an insulating touch with double-purpose models. Depending on your needs and activity, the outer layer should be chosen according to your needs and level of activity: it can be less or more protective, light, functional, warm and resistant.
Once you have all your gear, you'll enjoy the flexibility that this three-layer system provides. You can add or remove a layer depending on the weather conditions and the intensity of your efforts.