Anatomically shaped to provide protection, heat and compression for lower limb injuries, including calf strains, shin splints and Achilles" tendonitis. Thermoskin Thermal Supports utilize the exclusive Trioxon lining that is clinically proven to capture your natural body heat. Unlike other products, Trioxon allows your skin to ventilate and remain comfortably dry even with long-term use. Competitive products trap the perspiration resulting in discomfort, slippage, risk of infection and unpleasant odor. The Trioxon lining creates a microclimate to help the skin breathe while still providing effective heat therapy. This is the secret of Thermoskin"s long-term comfort for the user. You can even wear Thermoskin for extended periods of time without the discomfort you would have with other products. Sizing Guide: Measure circumference around calf muscle. X-Small 10 1/4 - 11 1/2 Inch. Small 11 3/4 - 13. Medium 13 1/4 - 14 3/4. Large 15 - 16 1/4. X-Large 16 1/2 - 18. XX-Large 18 1/4 - 19 3/4. If in doubt on Thermoskin sizing it is generally best to select the larger size.