The ECWCS (Extreme Cold Weather Clothing System) zip-collar shirt is extremely warm. The 100% polypropylene material will wick the moisture away from the skin. The Polypro long underwear have a smooth outer cover with a fleeced inside for extra warmth. The polypro thermal top features a zippered collar that forms a turtleneck or lies flat. The thermal top meets US Military Spec Plus. They are machine washable. However, they will stay nicer if you do not dry them in the dryer. The specifications include the following: 10oz. heavy expedition weight material, flat locked construction, hemmed cuffs with thumb holes in the sleeves to aid in adding multiple layers and one piece turtleneck style zippered collar. The thermals are available in sizes Small - XXXLarge.