Cold packs are used to treat injuries such as muscle sprains and strains. Cold packs are the commercial equivalent of ice packs. There are three types of cold packs: gel packs, instant cold packs and instant cold gel packs. The gel packs are simply filled with coloured gel and are frozen or refrigerated until needed. The instant cold packs and instant cold gel packs are more complicated and can be used one time, anywhere, without refrigeration.
Gel packs are simply pouches of polymer gel, the same gel used in baby diapers according to Custom GelPax Inc., which can be "frozen" and still remain pliable. These are placed in a regular freezer and used when needed. According to US Patent 4462224, at least one brand of this type of cold pack is made of water, propylene glycol and hydroxpropyl methylcellulose. A gel pack can usually be used as a heat pack by microwaving it. Refer to directions on the pack for details and safety precautions.
Instant Cold Packs
Instant cold packs have two or three compartments separated by breakable barriers. Each of the compartments contain an ingredient which, when mixed with the other ingredients, chemically react together to create a cooling effect. When the cold pack is needed, the user breaks the barriers by bending the pack and squeezing the contents together.
Ingredients of Instant Cold Packs
According to CPR Savers and First Aid Supply, instant cold packs are comprised of ammonium nitrate and water, each contained in a separate compartment. The chemical reaction between the ammonium nitrate and water causes a temperature drop to -23ºC/-9ºF within a few seconds. The temperature remains cold for 20 to 30 minutes. These are not reusable and should be disposed of after use.
Instant Cold Gel Packs
The instant cold gel pack combines the benefits of both types of cold packs. Generally comprised of three compartments, the ingredients are mixed together when the barriers are broken. The ingredients create an instant cooling effect, just like the instant cold packs, and form together into gel. The addition of the gel allows them to be reused as a gel pack later, making them more cost-effective. For reuse, place them in a freezer until needed.
Ingredients of Instant Cold Gel Packs
According to US Patent 4462224, the first compartment contains a solvent such as water and propylene glycol. The second compartment contains a solute, usually ammonium nitrate. The third compartment contains a gelling agent, such as hydroxypropyl methylcellulose, which combines with the solvent and solute materials and will remain soft and mouldable down to -18ºC/0ºF.