Original Heat Wave Instant Reusable Heat Packs provide therapeutic pain relieving heat in seconds and are reusable for a lifetime. All Heat Wave products are portable, so they can be used at home or office, while driving or commuting, or while attending or playing sports. Heat Wave medium and large rectangular packs can be used for: Ankle, calf, knee, thigh, and back pain; general muscle soreness and menstrual cramps. ((Our hand warmers fit comfortably in a pocket or in mittens. Heat Wave universal back / neck / shoulder / packs with conforming slits can be used for all large muscle group pain and soreness, stress relief, back pain, neck pain, and shoulder soreness.)) All of our original heat packs are designed to keep your bodies warm on demand. EcoFriendly + Cost Savings. We tested Heat Wave Instant Reusable Heat packs and stopped counting at 500! You never need to buy another heat pack. If you have been using disposable hand warmers or wraps, you only get one use. They get tossed in a landfill, with iron metal shavings making their way into the ground water. But with Heat Wave, one purchase and you are set for life! Heat Wave instant Reusable heat packs generate plenty of heat through a physical process. Simply flex the metal disc activator inside the pack, and start the heating process. Heat Wave Instant Heat Wraps reach a soothing 130 degrees. Note that if you are purchasing Heat Wave products or other instant reusable heat packs from companies other than Bent Grass Concepts, you might be receiving a counterfeit or inferior brand. Boil for 25 minutes and simmer for 10 to reuse.