What cold packs are used for
Popular and effective in treatments to ease pain and swelling from minor injuries, cold packs come in many different varieties. Some are sacks of gel that turn into ice packs in your freezer; others are packets designed to turn cold instantly with a simple squeeze, no refrigeration or freezing required.
Cold packs are very effective at reducing swelling and numbing pain. An injury swells because fluid leaks from blood vessels; cold causes vessels to constrict, reducing their tendency to ooze. The less fluid that leaks from blood vessels, the less swelling results. Cold also eases inflammation and muscle spasms, two common sources of pain.
The sooner you apply an ice pack to a sprain or strain, the sooner it can do its job reducing pain and swelling. For chronic problems such as low back pain or muscle spasms, ice whenever the symptoms start up. http://consumer.healthday.com/encyclopedia/first-aid-and-emergencies-20/emergencies-and-first-aid-news-227/ice-and-heat-packs-645144.html http://www.ebolagrandchallenge.net/instant-cold-packs/
No need for electricity like the solutions involving vents/freezers (scarce in some places Africa); no need for prior cooling (like dry ice/gel packs based solution) or special transport/storage
Main ingredients in the packs today are ammonium nitrate/urea (fertilizer ingredients) + water (+pack)
An ice pack or gel pack is a portable plastic sac filled with water, or refrigerant gel or liquid. For use the contents are frozen in a freezer. Both ice and other non-toxic refrigerants (mostly water) can absorb a considerable amount of heat before they warm above 0°C, due to the high latent heat of fusion of water.