Long Underwear 101
The purpose of long underwear is twofold. First, it is designed to wick sweat and moisture away from your skin. Second, it insulates you. Both are important, but depending on your activity, either wicking or insulating becomes your long underwear’s primary goal.
Weight/ Thickness: There are three different weights of long underwear, lightweight (often called silkweight), midweight, and heavyweight. The purpose of lightweight long underwear is almost strictly to wick moisture away from your skin. Midweight long underwear both wicks and insulates. Heavyweight long underwear is primarily designed to provide insulation, but it also manages moisture.
Activity: Keep in mind that a proper layering system is necessary depending on the weather and that this guide is strictly for base layers.
For high-aerobic activity, even in cold weather, your primary goal is to keep the sweat your body is producing away from your skin. If the sweat stays on your skin, you will experience evaporative cooling, and no matter how many layers you wear, you will still be cold. Therefore, a thin long underwear piece, most likely made out of a synthetic material (see below), would be the best choice.
For moderate activity in any type of weather, the best option is a midweight piece, made out of any non-cotton material (wool, Cocona, synthetic) that will keep moisture away from your skin and help keep you warm.
During low-aerobic activities (hanging out at camp, cooking, etc.), your long underwear is mostly just to keep you warm. A thicker piece made out of whatever feels best against your skin is the optimal choice.
Materials: The main thing with long underwear is that it is not made out of cotton. Yes, you can purchase cotton long johns at Wal-Mart, and they will work great for car camping in 40 degree nights. However, if you are planning to sweat, at all, then opt for anything other than cotton.
Wool – since manufacturers can now de-barb wool it is no longer itchy, and naturally provides great insulation and moisture management. Most of the wool for all the manufacturers (Smartwool, Ibex, Icebreaker) all comes from the same sheep in New Zealand, so pick a brand that fits well and stick with it. Yes, it’s a bit more costly than most of the synthetic pieces, but unlike synthetics, it’s incredibly durable, and mostly odor-resistant.
Cocona – made out of “upcycled” coconut shell husks and blended with polyester, Cocona has fantastic moisture wicking abilities and is naturally antimicrobial (you won’t stink). Many manufacturers are using Cocona because it is soft, comfortable, and fairly inexpensive.