A Rubber Band Gets Warmer When You Stretch It, And Colder When You Let Go

This backwards little experiment fits in your hands and quietly breaks the rules you'd expect.

Grab a thick rubber band and press it to your upper lip, then stretch it fast. You'll feel it warm up. Let it snap back to relaxed, and it actually turns a touch cooler.

Most materials get colder as you pull them apart, but rubber is a rebel. Its long, tangled molecules straighten out under stress, and that ordering releases a little heat.

When you release the band, those molecules jumble back into their messy natural state. Reorganizing takes energy, so the rubber pulls heat back in and cools down in your fingers.

It's one of the simplest weird-science demos you can do with pocket change. No lab, no gear, just a rubber band and your own lip proving that stretching can be a heat machine.