Duofold Originals - Long-Sleeve Crew Sweatshirt nylon, cotton base-layer-underwear closure 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. Close-to-body fit allows for easy layering. Details include tag-free banded crewneck and non-chafe flat-locked seams. Fiber Content: "100% Cotton inside / 65% Cotton, 25% Merino wool, 10% Nylon outside"