How Cool Packs & Hand Warmers Work

Everyone uses a cool pack at some time for an injury these days. They come in many different sizes and all use a chemical reaction producing an endothermic reaction (absorbs heat to go cold).

Ammonium Nitrate and Water can create the endothermic reaction as well as Sodium Carbonate and Ethanoic Acid.

A cool pack looks like this usually:

Cross Section of a Cool Pack


Reusable hand warmers come in many shapes and sizes and even colours! But do you actually know why they work and why they have that silver disk?

Well all they are made out of are;

  • A Disc
  • Water
  • Sodium Acetate (Food-grade salt ingredient)

When in a plastic pouch it looks like this:

Cross Section of a Hand Warmer


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One Reply to “How Cool Packs & Hand Warmers Work”

  1. Wow, I never realised that the cool packs in school actually created a chemical reaction to help cool down our injuries!

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