The Smartwool Classic Thermal Merino Colorblock Base Layer is designed for comfort and performance in cool-to-cold temperatures. Flatlock seam construction minimizes chafing, while shoulder panels eliminate top shoulder seams. Made from 100% Merino wool, the fabric provides enhanced breathability, thermoregulation, and odor resistance. With a Classic Thermal temperature rating for use in conditions 50°F and below, this base layer keeps you warm and dry during your cold weather activities.