In nearly every outdoor activity you undertake in fall, winter and spring, a good base layer can keep you more comfortable, allowing you to have more fun enjoying the great outdoors. As most avid outdoorsmen know, cotton “thermal underwear,” which used to be called “long johns,” just won’t cut it anymore for staying warm and dry during cold-weather activities. But the wide variety of base layer styles, materials and temperature ratings available can be confusing if you don’t understand the terminology and the general idea behind layering. To make a good selection when shopping for a base layer, consider three important factors—fit, moisture wicking qualities and weight of the base layer.

Great Value

This one is anti-static, anti-odor and fast-drying. Amazon

Base layers are far from being one-size-fits-all garments. If your base layer is oversized and saggy, it’s not going to provide you with all the benefits a good-fitting base layer will. That’s also true for undersized base layer garments, which can cut into your arm and legs at the cuff, restrict your movement and be very uncomfortable. For a base layer to wick properly—either upper or lower—it needs to lay against the skin in order to pick up moisture. Consequently, the fit needs to be relatively snug. One exception is when wearing a base layer as your only upper garment for cool-weather outdoor activities. In that case, a looser lightweight base layer top might be more comfortable than a form-fitting one.

Top Pick

Its four-way stretch construction allows easy movement in all directions. Amazon

Wicking is a fancy word for saying your base layer garment draws sweat away from your body and pushes it outward, keeping your skin dry. Since the surface area of wicking materials is much greater than that of some natural fabrics like cotton, it is easier for moisture to evaporate from them, leaving you warmer and drier. The wicking ability of base layers ranges widely depending on the fabric. Garments made of a high percentage of polyester mixed with spandex and/or nylon wick the best. At the other end of the spectrum is cotton, which has zero wicking ability. If you sweat when wearing cotton as a base layer, or garments made of a higher percentage of cotton, you might stay warm, but likely won’t be dry and comfortable.

Also Consider

Its silky-soft inner fabric provides extra comfort and heat. Amazon

Base layers are marketed for different activities and conditions based on weight—lightweight, midweight and heavyweight. For lightweight base layers, thinner is better. They might not provide much insulation, but if it’s just cool outside, you might be wearing them more for their wicking ability anyway. Base layers labeled as “midweight” can be used either as a next-to-the-skin first layer or as a second layer in colder weather. They wick well and provide thermal protection in moderately cold conditions. Base layer garments labeled “heavyweight” are made for extremely cold conditions and are typically much thicker than other base layer garments. Since they are usually worn as a second or third layer, their wicking ability isn’t as important as the ability to help keep you warm when most other adventurers have gone inside to sit by the warm fire.