Does hot water really freeze faster than cold water?

It sounds like it breaks common sense, but in certain setups a warmer body of water reaches freezing before a cooler one starts to. The phenomenon is named after Erasto Mpemba, a Tanzanian student who noticed his hot ice-cream mix froze faster than a cold one.

Several things likely combine to cause it. Warm water evaporates faster, so there’s slightly less of it left to freeze. Dissolved gases escape as water heats, which can change how it cools. And convection currents in the warmer water move heat to the surface more efficiently, where it’s lost.

The catch is that the effect is finicky. It depends on container shape, how the cold is applied, and how you define “frozen,” and plenty of careful experiments fail to reproduce it. So treat it as a genuine curiosity rather than a reliable trick for making ice faster.