What Is the Blue Stuff in Reusable Cold Packs?

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Reusable cold packs have made cooling bumps and bruises or relieving pain more convenient than using ice wrapped in towels. In addition to first-aid uses, these packs can help keep food cool for hours when travelling or taking a day trip or even shipping food or refrigerated medicine.

While the packs may melt, the contents will not leave the same wet mess as melted ice. The contents found in blue ice packs consist of water that is mixed with ammonium nitrate fertiliser or a combination of other chemicals.

Ammonium Nitrate Fertilizer

Used commonly by farmers, this fertiliser is made of nitrogen and calcium carbonate. Used in instant cold packs, an endothermic reaction (a reaction that absorbs heat) occurs when the pack is cracked and shaken and the temperature of the packs drops to approximately 1.67 degrees Celsius for 10 to 15 minutes. Although useful as a fertiliser for the farming community as well, the unstable combination of these chemicals can also lead to dangerous accidents and harmful events. For example, in 1995, this fertiliser was ignited in the Oklahoma City Bombing, which razed the city’s Federal Building and killed several hundred people.

Reusable Cold Packs

The more common reusable cold packs have a blue gel contained in a sealed bag. According to the 3M Reusable Cold Packs Material Safety Data Sheet (MSDS), these noncombustible ingredients are primarily water (60 to 70 per cent), propylene glycol (20 to 35 per cent) and sodium carboxymethyl cellulose (less than 5 per cent), with a polypropylene cover.


Although advertised as nontoxic, the chemicals contained in a reusable cold pack may cause mild eye irritation, localised redness of skin or, if ingested, abdominal pain, stomach upset, nausea, vomiting and diarrhoea. Side effects of ingestion may include headache, dizziness, drowsiness, lack of coordination, nausea and slowed reaction time, among others.

First Aid

It is advised to seek medical attention if the contents of a reusable cold pack come in contact with the skin or eyes or is ingested. If contact is made to the eyes or skin, wash with large amounts of water. If ingested, do not induce vomiting. Rather, give the victim two glasses of water and seek medical attention. If the victim is unconscious, seek medical attention prior to anything else.

Homemade Cold Packs

To make your own cold pack, add 3 cups of water and 1 cup of isopropyl alcohol to a zip-locking plastic bag. Close the bag and insert it into another zip-locking bag. Place it in the freezer. The contents will become a slushy frozen mixture. A cloth should be used over the cold pack when applying it to the skin.