Ice pack

The instant type is generally limited to medical use as a cold compress to alleviate the pain of minor injuries, while the reusable type is both used as a cold compress and to keep food cool in portable coolers or in insulated shipping containers to keep products cool during transport.

Water has a much higher latent heat of fusion than most substances, and a melting temperature which is convenient and easily attained with, for example, a household freezer.

They can be used as a normal reusable ice pack by storing in a freezer, but they can also be heated in water or a microwave oven to reach the desired temperature.

[3] The first reusable hot cold pack that could be heated in boiling water or a microwave oven was first patented[4] in 1973.

When the inner bag of water is broken by squeezing the package, it dissolves the solid in an endothermic process.