The Wonder Pax Reusable Cool/Warm Gel Pack For The Back- Blue

It provides effective relief for muscular and joint aches and pains. It can be used as a cold compress (refrigerated) or a hot compress (activated by flexing an internal metal disc). The non-toxic solution heats up instantly to 130°F (54°C) and stays hot for up to an hour. The pack is reusable; boiling it in water reverses the crystallization process so it can be used again and again. It is designed to cover the back, spine, and lumbar area, among others.