Cool58 cooling packs freeze solid at a moderate and comfortable temperature of 58° Fahrenheit (14.4° Celsius), so they can be frozen in a freezer, refrigerator, or even a cooler of ice water. Once activated, these reusable packs deliver comfortable cooling for up to 2 hours. (Please note: cooling times are estimates and will vary depending on climate, body metabolism and activity.) Packs are non-toxic and non-flammable. Packs do not require a freezer! Packs can simply be submerged in ice water or placed in a refrigerator or freezer to activate. Easy to use - packs can be activated by simply submerging the packs into ice water for up to 20 minutes when access to freezers is not available. Works in any climate - extreme heat and humidity are no problem! The cooling performance is not impacted by humidity or outside temperature.