Thermoskin Flexible Thumb Splint is easily moldable and supports the carpometacarpal (CMC) joint, while providing heat therapy and rigid support for ulnar collateral ligament (UCL) injuries associated with ball sports, skiing and repetitive strain (RSI). Trioxon Advantage: Thermoskin"s exclusive Trioxon lining is soft and comfortable against your skin. Trioxon captures your natural body heat for therapy and pain relief. The three dimensional Trioxon lining provides insulation and wicking of moisture via air circulation. This allows the skin to remain well oxygenated and comfortable for extended periods. Clinically Proven: Only Thermoskin is clinically proven to increase blood flow, increase skin temperature, increase muscle temperature, and minimize perspiration. Available in Small, Medium, and Large. Sizing Guide: Measure the circumference around the wrist joint. Small 4 3/4 - 6 1/4 inches. Medium 6 1/2 - 7 1/2. Large 7 3/4 - 9 inches. If in doubt on sizing for Thermoskin products it is generally best to select the larger size.