An ice pack or gel pack is a plastic sac of ice, refrigerant gel or liquid, or, in an emergency, even frozen vegetables. The refrigerant, usually non-toxic, can absorb a considerable amount of heat, since its enthalpy of fusion is high. It is commonly used as a cold compress to alleviate the pain of minor injuries or in coolers or insulated shipping containers to keep products cool during transport. The simplest type of ice pack is simply a sack, bag or towel filled with cubed or crushed ice.
Ice packs are used in coolers to keep perishable foods (especially meats, dairy products, eggs, etc.) below the 41–165 °F (5–74 °C) danger zone when outside a refrigerator or freezer. If the foods and the ice packs are placed in a cooler directly from the freezer, then the equivalent of 10 to 20 pounds of ice is needed for each 24 hour period. If the foods start off warmer (for example, non-frozen food from a refrigerator), they will not be able to remain safely cool for as long.
Water (ice) has an unusually high enthalpy of fusion and a convenient melting temperature (one accessible by household freezers). However it isn't ideal for ice packs for various reasons, so additives to improve the properties of water are often used. For example, substances can be added to prevent bacterial growth in the pack, as can additives that cause the water to remain a thick gel throughout use, instead of transitioning between a solid and a free-flowing liquid like plain water. These gel packs are often made of non-toxic materials that will not liquefy, and therefore will not spill easily or cause contamination if the container breaks. Gel packs may be made by adding hydroxyethyl cellulose (Cellusize) or vinyl-coated silica gel.
These gel packs, as with ice itself, are chilled before use. The gel-pack or water is placed in a freezer or other cooling system to lower its temperature, and then it is used to keep other items cool. Ice packs are effectively a device for storing cooling capacity.
Another type of ice pack uses an endothermic reaction to cool down quickly. These types of ice packs are stored at room temperature rather than needing to be physically cooled before use. When one breaks a tube inside the pack, two chemicals mix or react and absorb enough energy to produce a cooling effect. Common types include solid ammonium nitrate, or ammonium chloride dissolving in water.
The reusable hot cold pack was first patented  by Jacob Spencer of Nortech Labs in 1973 (Patent No. 3,780,537). Reusable hot cold packs differ from instant cold packs in that they can be either frozen or microwaved.
- ^ "Versa-Pac™ Reusable Heavy Duty Cold Pack" (PDF). Unipatch. Tyco. February 2004. http://www.uni-patch.com/PDF/MSDS_ReusableHD.pdf. Retrieved 2009-06-01. [dead link]
- ^ "CELLOSIZE Hydroxyethyl Cellulose (HEC)". UCAR Emulsion System Products. Dow. http://www.dow.com/ucarlatex/prod/cello/. Retrieved 2009-06-01. [dead link]
- ^ Niss, Jan (September 26, 2008). "Ice pack or cold pack". Healthwise. MSN health & fitness. http://health.msn.com/health-topics/articlepage.aspx?cp-documentid=100063410. Retrieved 2009-06-01.
- ^ "#7 – Hot Pack / Cold Pack". Science Activity. Howard Debeck Elementary School. http://nobel.scas.bcit.ca/debeck_pt/science/hotColdPack/pack_p1.htm. Retrieved 2009-06-01.
- ^ "How Refrigerators Work: Cold Packs". http://home.howstuffworks.com/refrigerator7.htm. Retrieved 2010-06-28.
- ^ Nortech Labs History - Patent of Reusable Hot Cold Pack, Dec. 25, 1973, Patent No. 3,780,537 [Nortech Labs History | http://www.nortechlabs.com/nortech-history.html]
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Ice pack — Ice Ice ([imac]s), n. [OE. is, iis, AS. [=i]s; aksin to D. ijs, G. eis, OHG. [=i]s, Icel. [=i]ss, Sw. is, Dan. iis, and perh. to E. iron.] 1. Water or other fluid frozen or reduced to the solid state by cold; frozen water. It is a white or… … The Collaborative International Dictionary of English
ice pack — n 1.) a bag containing ice that is put on injured or painful parts of your body to keep them cold 2.) a large area of crushed ice floating in the sea →↑pack ice … Dictionary of contemporary English
ice pack — ☆ ice pack n. 1. PACK ICE 2. an ice bag, folded cloth, etc. filled with crushed ice and applied to the body, as to reduce a swelling or ease pain … English World dictionary
ice pack — ice′ pack n. 1) geo pack ice 2) med ice bag • Etymology: 1850–55 … From formal English to slang
ice pack — ice ,pack noun count 1. ) a bag full of ice that you hold against an injured or painful part of your body to stop it from swelling or make it less painful 2. ) an area of small pieces of ice floating in the ocean … Usage of the words and phrases in modern English
ice pack — ice packs N COUNT An ice pack is a bag full of ice which is used to cool parts of the body when they are injured or painful … English dictionary
ice pack — ► NOUN ▪ a bag filled with ice and applied to the body to reduce swelling or lower temperature … English terms dictionary
ice pack — noun 1. a waterproof bag filled with ice: applied to the body (especially the head) to cool or reduce swelling (Freq. 1) • Syn: ↑ice bag • Hypernyms: ↑bag 2. a large expanse of floating ice • Syn: ↑pack ice … Useful english dictionary
ice pack — UK / US noun [countable] Word forms ice pack : singular ice pack plural ice packs 1) a bag full of ice that you hold against an injured or painful part of your body to stop it swelling or make it less painful 2) an area of small pieces of ice… … English dictionary
ice pack — noun a) a large floating mass of ice; pack ice b) a pack of crushed ice applied to the body in order to reduce pain or inflammation … Wiktionary