The Castelli Pro Issue Sleeveless Base Layer is ideal for cool to mild conditions. It wicks moisture away from the skin leaving you feeling drier and more comfortable. This isn\'t a thermal base layer, just something to move the moisture away from your body and help your race jersey perform. Castelli\'s 3D mesh fabric creates air space next to your skin, while the polyester capillary action moves sweat away. Key Features 100% polyester 3D mesh fabric Reduced seaming at shoulders for extra comfort Wider collar to fit under aero jerseys Flat waist hem to lie flat in shorts Sizes men\'s XS-2XL Weight 44g (large) Castelli comfort range 15-30C