HeatGear fabric wicks sweat away from your skin to keep you cool, dry & light. Dual density EVA foam for increased impact protection. Hinged design allows for maximum mobility. Small: 10.2" Top Circumference, 9.1" Bottom Circumference. Medium: 11.4" Top Circumference, 9.8" Bottom Circumference. Large: 12.6" Top Circumference, 10.6" Bottom Circumference.