ColdStar all-purpose hot and cold therapy gel packs are ideal for treating sore muscles, achy joints, swelling, and more. They can be microwaved for heat therapy or frozen to create an ice pack. The soft freeze gel stays flexible when frozen, which allows the cold pack to conform to the contours of the injured area. ColdStar cryotherapy gel packs are reusable and are a great addition to a first aid kit.