Outdoor clothing can be made from different fabrics, as well as a number of different fabric combinations, and are sewn or knitted using different techniques. Each fabric and combination of fabrics has its own unique characteristics. When choosing winter clothing, it is necessary to understand what the advantages and disadvantages of each fibre are in the environment where they will be worn.
Wool is a natural material that has many properties that are useful in a winter environment. The curly, hollow structure of the fibre binds a lot of air, which provides insulation. Wool absorbs moisture and wicks it through the fabric and into the fibre itself, which means that a wool garment feels dry against the skin and provides insulation even when damp. Another benefit with wool is that it does not smell in the same way synthetics do. Wool is excellent in socks, underclothes and middle layers.
One of wool’s downsides is that the rough wool fibres can feel scratchy. Underclothes are therefore usually made of a softer wool from merino sheep. (People with sensitive skin can also have problems with finer wools, so it is important to thoroughly test the layer of clothing closest to the skin. An alternative to merino wool is silk or synthetics.)
Synthetic fibres are created using a chemical process that often relies on oil as one of the raw materials. Typical examples are polyester, polyamides and polypropylene. Depending on how the fibre is designed it takes on different properties, but in general synthetic fibres are good at wicking away moisture while being durable and long-lasting. For this reason, synthetics are often mixed with natural materials, for example in wool base layers.
Synthetics are used for all layers of clothing, from underclothes to shell garments. Synthetic base layers are perfect for physical activities and people who sweat easily and profusely. Middle layers made from synthetics, such as a fleece sweater, also wick away moisture and dry quickly and the curly structure traps air which provides insulation. One downside of synthetics is that they are fast to emit a bad odour and lose part of their functionality if they are not washed frequently. All synthetic garments should also be worn with care around fires and sources of heat; the fabric is flammable and can melt at relatively low temperatures (for example, polypropylene shows signs of disfigurement at 90-100°C).
Cotton is a natural material and in general is the most common fabric used in clothing. But cotton binds moisture, takes a long time to dry and lowers your body temperature, which means it is not a good functional fabric for winter conditions, at least for the layers of clothing that are closest to the body, such as underclothes, socks, base layers and middle layers. That said, however, tightly woven cotton can be functional in outer garments in extremely cold temperatures, for example in an anorak, since the porous nature of the fabric helps release moisture from the body. The general rule of thumb is that “the further away from the body, the better cotton works in a cold and dry winter climate”.