Samm Men's NCAA BYU Cougars Compression Under Base Layer Sport Shirt 90% polyester-10% spandex. Excellent elasticity with enhanced range of motion. Adopting moisture transport system sweeps away sweat and dries quickl whick can keep you cool, dry, and comfortable. Sizes:S,M,L,XL,these sizes are standard American size. Super scalability, If you are a big muscle, Please order 1 Size Up than you normally wear on USA Size. Perfect option during various indoor activities and outdoor excursion.Like fitness exercises,body-building exercises,basketball running,sports training and etc.