The Smartwool Classic Thermal Merino Base Layer Bottom - Men's is a warm base layer for winter activity. Hike, ski, camp, the list goes on, and when it's cold, this 100% Merino wool layer is ready for action. The soft fabric is the warmest-weight available in the line, for toasty comfort in the outdoors. Remain focused on the adventure, while the fabric manages sweat, resists odors, and regulates temperature.