The Thermoskin Wrist Thumb Sleeve contains the exclusive Trioxon lining for clinically proven heat therapy. Thin stretch memory foam contours to the wrist and thumb for comfort. Combines warmth with compression to increase circulation and provide pain relief. Textured outer layer for additional grip. The medium size is great for hands measuring 8 to 9 inches (21-23 cm). In order to get the right size, measure the circumfrence around your knuckles. Universal design fits the right or left hand.