Champion Duofold by Men's Full Button Front Base Layer Union Suit Inside:100% Cotton. Imported 2-LAYER 6.3-OZ. FABRIC: 100% cotton inside 65% cotton/25% Merino wool/10% nylon outside 6.3-oz. fabric has two non-bulky layers. Outer layer contains Merino wool for natural insulation. Inner layer is pure cotton for softness next to your skin. Together both layers trap air to create a warm thermal barrier. Ribbed elasticized cuffs help seal out cold and chill. Flat-locked non-chafe seams feel smooth against your skin. Details include tag-free collar full-length button-down placket and convenient rear fly.