Base Layer
The goal of the base layer (wicking layer) is to keep your sky dry and comfortable. It is your first layer (against the skin) and it helps regulate your body temperature by transporting moisture from body perspiration away from the skin to the outside of the fabric where it can evaporate. In cooler weather, the base layer should be more close-fitting to provide extra insulation. In warmer weather, the base layer should be more loose-fitting (more loose-fitting, not loose-fitting) to maximize ventilation and absorb (or wick) moisture from the skin. The base layer your wear should dry quickly because keeping dry helps you maintain a cool body temperature in the summer and avoid hypothermia in the winter. There are a variety of different ways to transport moisture away from your body:
- Merino Wool Merino wool is a natural fiber. It is a heat releaser because it has a heat of sorption rate of four times that of nylon and at least twice as much as polyester. This molecular process releases heat back to your body and keeps you warm even if the wool itself is cold or damp. Merino wool also wicks moisture away from your body, although it is different than wicking fabrics. Because they do not absorb it, traditional wicking fabrics allow moisture to run through the fabric. Merino wool, on the other hand, is hydroscopic, meaning that it is capable of absorbing moisture and moving it away from your body while simultaneously repelling liquids. It can also hold up to 30% of its weight in moisture before it begins to feel damp. Examples: SmartWool, Ibex, and Icebreaker.
- Micro-channel Fibers Micro-channel fibers are synthetic fibers with very small channels, or capillaries, within the individual fabric threads. They depend on what is known as "capillary action" to transport moisture through the channels from next to your skin to the outside of the fabric. Some fabrics are bicomponent, meaning that they have an inner layer of macrofiber yarn and an outer layer of mircofiber yarn. The outer layer has a much greater surface, which in turn helps pull the water to the outside of the fabric. Examples include: CoolMax and Polartec PowerDry.
- Hydrophobic/Hydrophilic Fibers Hydrophobic/Hydrophilic fibers are synthetic fibers usually made of polyester or polypropylene that do not absorb water. They are effective when worn directly against the skin to both help keep it dry and reduce evaporative heat loss. Some of these fabrics are hydrophobic on the inside (they do not like water), meaning that they push the water vapor from your skin to the outside of the fabric. Other fabrics are hydrofphilic on the outside (they like water), meaning that they pull the water outward. Some fabrics are bicomponent, meaning that they use a hydrophobic inner layer and a hydrophilic outer layer. Examples include: Capilene, Lifa, and Dryline.