Freezer gel packs are a convenient way to keep things cool for extended periods of time. Often times they work equally well as hot packs. They’re used for a variety of purposes including shipping, muscle warmth or cooling, and school lunches. The stuff inside them isn't dangerous and is designed to change with temperatures.
Inside freezer gel packs, as you may have guessed, is gel. Common gel types are hydroxyethyl cellulose, polymer, or silica coated with vinyl. This gel is non-toxic and biodegradable. The amount of gel inside freezer gel packs varies depending on the type of gel and size of pack.
While always soft and squishy when it's hot or at room temperature, some gel hardens solid when frozen and some remains malleable. The gel has a lower freezing point than water, so the pack will stay colder longer. Also, some gels are formulated to have different freezing temperatures than others. A common freezing point is 32 degrees Fahrenheit, but gel is available with a freezing point at 10 degrees Fahrenheit.
Some additives help the gel do its job. These additives include preservatives, sodium chloride, minerals, and water. Some freezer gel packs also contain dye to color the contents.
Inside Homemade Gel Packs
There are also homemade versions of gel packs, which don’t require the silica or polymer gel. These packs are made from a mixture of rubbing alcohol and water and put in freezer bags. The water freezes while the alcohol does not, which creates a squishy gel like feel. It keeps cooler for longer than if the pack contained only ice. These packs only work as freezer packs, not as hot packs.
The gel in freezer gel packs is non-toxic, so should you puncture your pack, or it tears, the gel will do no harm. If you own a pack that has an especially low freezing point, the gel pack may cause a mild freezer burn. The packs are designed so they will not get hot enough to burn. Nevertheless, place a towel or thin cloth around the pack before applying it to skin unless the pack has a thick cover already. Clean any spilled gel up completely because the gel is very slippery.