heated in boiling water or a microwave oven was first patented in 1973. Instant ice packs An instant cold pack is a single-use device that consists of two bags; one containing water, inside a bag containing ammonium nitrate, calcium ammonium nitrate or urea. When the inner bag of water is broken by squeezing the package, it dissolves the solid in an endothermic process. This process absorbs heat from the surroundings, quickly lowering the pack's temperature. Instant cold packs are a convenient replacement for crushed ice used as first aid on sport injuries or heat illness, and can be carried as first aid to remote or wilderness areas where ice is unavailable. However, they do not provide as much or as long-lasting cooling as ice. Safety concerns Gel packs have been made with diethylene glycol and ethylene glycol. Both can cause illness if ingested in large amounts, making them unsuitable for use with food. The US Consumer Product Safety Commission recalled such packs. See also Cryotherapy Hot pack Hand warmer Hilotherapy Phase-change material Enthalpy of fusion References Medical treatments Cooling technology Food preservation Medical equipment Cryotherapy Packaging