Reusable heat packs are devices that can be used to apply heat to the body. They are often made using soft plastic, which is filled with a gel. The soft plastic is often encased in padding to prevent too much heat from being applied to the surface of your body. When microwaved, the gel will start to warm up, and when the pack is applied to the skin, this heat will radiate out to surrounding areas and provide relief from pain or inflammation. Once the heat pack has cooled, it can be reheated and reapplied to your body.