This 4 pack of new 3 x 6 inch Heat Wave XT heat packs are extra large and extra long lasting, lasting 40% longer; packed with extra heating power, weighing 40% more than our 3 x 5 hand warmer, in a size 20% larger. All Heat Wave instant heat packs provide therapeutic pain relieving heat in seconds and are reusable for a lifetime. Heat Wave products are portable, so they can be used at home or office, while driving or commuting, or while attending or playing sports. Our hand warmers, whether Original 3 x 5 or New 3 x6 Heat Wave XT, fit comfortably in your hands or pockets. Our other products include medium and large rectangular packs to be used for large joint and back pain; muscle soreness and menstrual cramps. The universal neck / shoulder / back packs with conforming slits can be used for all large muscle group pain and soreness, stress relief, back pain, neck pain, and shoulder soreness. Pro Heat on demand. 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 good to go! 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. We protect the metal disc with plastic for safety, our material is thicker than competitors, and we contain more fluid per size of any other heat pack, making it longer lasting. 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 other companies, you might be receiving a counterfeit or inferior brand. Heat Wave is a registered trademark of Bent Grass Concepts. Boil for 20 minutes with a rag in the pot, then simmer for 10 to reuse.