The effectiveness of any layering system is in its foundation - the layer nearest the skin. It has to insulate when activity is low, then wick moisture away from your skin as perspiration builds with activity. Browning Hunderwear is ideally suited to be the base of any layering system. - 97% polyester, 3% X-Static - X-Static is a natural anti-microbial, anti-static material that reflects heat back to the body and disburses it through thermal conductivity _________________________________ Men's Apparel Sizing Information: Small: Chest = 37-39", Waist = 38-31", Neck = 14-14.5", Arm = 32-33" Medium: Chest = 40-42", Waist = 32-35", Neck = 15-15.5", Arm = 33-34" Large: Chest = 43-45", Waist = 36-39", Neck = 16-16.5", Arm = 34-35" XLarge: Chest = 46-48", Waist = 40-43", Neck = 17-17.5", Arm = 35-36" XXLarge: Chest = 49-51", Waist = 44-46", Neck = 18-18.5", Arm = 36-37" XXXLarge: Chest = 52-54", Waist = 47-49", Neck = 18-19", Arm = 36-37"