Coldpruf Men's Authentic Cotton/Merino Wool Long Sleeve Henley Shirt ( Sizes: M-2X) 18 Layer Engineering Traps Air Providing A Natural Barrier of Warmth INSIDE: 100% Combed Ring Spun Cotton OUTSIDE: 65% Combed Ring Spun Cotton, 25% Merino Wool, 10% Nylon Can be worn as a base layer or just as a regular shirt