Cold packs, also called ice packs or gel packs, are enclosed sacs of ice or refrigerant used to maintain temperature of a surface or packaged item.
The endothermic reaction of a cold pack results in its absorption of nearby warmth. Cold packs consist of a pliable pouch, often nylon, polyurethane or latex, withholding a chilled refrigerant. Reusable cold packs with a hard plastic, non-pliable shell are produced as well.
In reusable cold packs the refrigerant is usually a freezable gel of silica gel, hydroxyethel cellulose or polymer. Also included can be preservatives to prevent bacteria growth and water to aid freezing. Some cold packs elect to use ice cubes for every application, rather than a packaged refrigerant. Instant cold packs are fashioned of two chambers with a smaller bag inside the larger pack: one containing water and the other with ammonium nitrate or ammonium chloride. When an instant cold pack is squeezed the inner pouch is ruptured, mixing the agents and causing a chemical endothermic reaction. Makeshift cold packs can be made of ice and a sandwich bag.
The urgency of cold pack use dictates which cold pack to utilize. Instant cold packs are typically found in first-aid kits for emergency use to reduce pain and swelling. Due to its chemical composition they are not used to keep food cold. To alleviate anticipated discomfort reusable cold packs can be prepared, and due to its non-toxic contents are also suitable for food preservation.