These Instant Ice Packs are simple and easy to use with no mess and nothing to prepare. Great for use within first aid kits and to keep in gym bags.This Instant Cold Pack provides relief of pain and inflammation, single use only. Just break the water bag inside and shake, the temperature of the pack will rapidly decrease until reaching temperatures below zero. Best wrapped in cloth to prevent cold burn. Can remain cold for up to 2 hours depending upon the ambient temperature.