Are Cooling Blankets a Real Thing? The Physics of Making Something Cool.

Photo: Rhett Allain. Ice, blanket, and fire.

I know summer is over (but it’s still hot here) so that you might soon stop seeing all of these promotional videos for “cooling blankets”. People say they are like magic — just throw it on top of you and it cools you off. Oh, no wait — you have to get a REAL one. The one you got is fake.

So, I had to get one of these blankets to try it out. Do they really work? If they don’t work, is there something that WOULD work? Let’s do this.

How Do You Make Things Cool?

Suppose you have an object — maybe it’s a bottle of water. If you want to make the bottle colder, there’s really only one way to do this — put it in contact with something that’s colder.

Here’s an actual example. I have a block of plastic that’s 40 C in contact with an iron cube at 20 C.

Photo: Rhett Allain. A hot block in thermal contact with a colder block.

Energy will always be transferred from the hotter object to the colder one (it’s actually weird that this happens). But since the plastic loses energy, it will decrease in temperature and the iron will increase in temperature. Notice also that the iron block might actually have MORE energy even…