When it comes to your comfort level in the great outdoors, the base layer is the foundation of your entire layering system. Whether you ski, snowboard, climb or backpack, your women’s base layer should be breathable, lightweight and fast drying. Women’s base layers, also called thermal underwear and long underwear, breathe and wick moisture away from the skin during exercise, which helps minimize overheating. Later, if you slow down or rest, your base layer will dry quickly to help lock in warmth. Women’s long underwear comes in a variety of performance materials, such as silk, polyester and merino wool, all fabrics that transfer moisture away from the skin and evaporate sweat much faster than cotton. For the best in women’s base layers and long underwear, check out Icebreaker, Terramar and Hot Chillys.