One excellent method for dressing in cold conditions is the multi-layer principle. This principle makes it possible to adapt to the cold, wind and rain. The multi-layer principle divides clothing into four layers, each with its own purpose:
Base layer – wicks moisture away from the skin
Moisture conducts the cold and lowers your body temperature. The base layer should transport moisture away from the skin and keep you dry and warm. In order to function well, the base layer should be rather close to the body. Good base layer materials include synthetics or wool, but cotton should be avoided (read more under Material basics). The no-cotton rule also applies to underwear, socks and bras.
Middle layer – absorbs and wicks away moisture and provides insulation
The second layer should continue to transport moisture away from the base layer while at the same ensuring there is no unnecessary heat loss. The air in the middle layer provides insulation and if temperatures are very low or your activity is stationary, a thicker layer with more air is needed. Fleece or wool sweaters make good middle layers, and it is a good idea to have zippers or other openings that can be opened to release excess heat.
Outer layer – protects against wind, rain and wear and provides insulation
The third layer is a wind and water resistant shell that simultaneously keeps the cold out and the heat from the inner layers in. It also integrates with the other layers by releasing moisture. The outer layer is worn when you are active and it should protect sensitive areas such as your head, throat, wrists, waist and ankles. It should be possible not only to open the neck, sleeves and ventilation openings to release damp heat, but also to open zippers and make other adjustments while wearing gloves.
Modern shell garments with membranes are popular, but in extremely cold temperatures their ventilation capacity is impaired, which means that moisture is trapped inside the garment and, in the worst case scenario, lowers your body temperature. In dry, cold environments, garments made from G-1000 or tightly woven cotton are a better choice since they release some of this moisture through the fabric.
Reinforcement layer – gives added protection when sitting still
Reinforcement garments are put on when resting or when it is time to set up camp. They can be worn both on top of and under a shell garment; an extra sweater or a thermal jacket/trousers with down or synthetic padding are excellent for this purpose. Pull-over garments should be roomy so they are easy to pull over your clothes. They should be stored in the pack where they are easily accessible so you really will put them on when you take a break.
It is easy to assume that a winter trek is synonymous with extreme cold, but in many mountain environments the weather can change dramatically, for example when coastal winds blow in wet snow or even rain. In this kind of unpredictable weather a reinforcement garment can be an ultra-light rain garment that is pulled over the third layer, the working garment, to protect against moisture. In other words, the multi-layer principle is a model that provides a basis for how to think when planning your trek. As with all models, it must be adapted to real-life situations and prevailing conditions.