Duofold by Champion Originals Heavyweight Men's Long-Sleeve Thermal Shirt-Tall 100% Cotton base-layer-underwear closure Lofty heavyweight fabric has two non-bulky layers. Inner layer is pure cotton, for softness next to your skin. Outer layer contains Merino wool for natural insulation. Together, both layers trap air to create a warm thermal barrier. Details include flat non-chafe seams, tag-free banded collar, and chill-blocking rib-knit cuffs. Customized fit for tall men. Fiber Content: "100% Cotton inside / 50% Cotton, 40% Merino Wool, 105 Nylon outside"