The Odlo Warm Shirt is a beautiful base layer made of 100% Polyester. The Polyester gives this shirt a number of useful properties, including good moisture transport and the fact that the shirt dries quickly. The lining of the shirt is brushed, which not only makes the shirt comfortable but also improves breathability. The flat-stitched seams prevent the shirt from chafing when you move. The back of the shirt is slightly longer, this prevents bare spots from falling when moving.