Ultimate thermal underwear. Count on this wool-blend union suit for warmth in very cold weather. 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.