Mystery #3Tier 2-3chemistry / energy

How does an instant cold pack go cold on its own?

You bang your knee, grab a flat pouch from the cupboard, give it a squeeze, and within seconds it's icy cold, without ever touching a freezer. Squeezing something doesn't normally chill it. So how does this pack turn cold all by itself?

A commercial instant cold pack pouch, squeeze it and a salt dissolves inside, turning it icy cold. — Photo: Qurren, Wikimedia Commons · CC BY-SA 4.0 · via Wikimedia Commons

Your guess

What's your hunch about how squeezing a pouch could make it suddenly cold?

There's no single magic word to type, have a go in your own words, then reveal the answer to see how close you got.

Make a guess to unlock the hints and the answer.