This Heat Wave Instant Reusable Hand Warmers 2-Pack, originally $40, is now $12.99 at Tanga. Plus, shipping is free making this the best price we found for these by at least $17. Once triggered, the instant crystallization process of these hand warmers produce heat up to 130 degrees Fahrenheit within seconds. The packs will actually change from liquid to solid, conforming to your body, emitting heat through the physical change. These heat packs can produce therapeutic heat for up to two hours or more, depending on heat pack size and application. Sales tax is charged in most states.