The ThermiPaq Icy Cold Pain Relief Wrap Large uses a thermal ceramic compound made from all-natural clay-based materials. Developed by a former NASA engineer it utilizes radiant energy to create a deep penetrating and therapeutic cold feeling to the application site. It transfers slowly and evenly to the affected pain area. The soft fleece sleeve wraps around the pack. It has a Velcro strap for a secure fit. You can easily place the wrap around your back knees ankles and elbows for effective relief. The ice cold wrap is portable and convenient.