Hot & Cold Therapy Packs are used to provide heat therapy and cold therapy for common sports injuries such as strains, sprains and pulled muscles. Filled with a gel, they can be either heated in a microwave or cooled in a freezer and applied directly to an injured part of the body. Cold therapy reduces pain and swelling from injuries, while heat therapy can soothe any pain, stiffness and cramp that persists after the first 72 hours.