The Evaporation Theory

One leading explanation focuses on evaporation. Hot water evaporates faster, which reduces the total volume of water that needs to freeze. Less water means less energy to remove before ice can form, so the smaller amount left behind reaches freezing sooner.

Evaporation also cools the remaining water through latent heat loss — the same cooling mechanism behind sweating. Less water at a lower starting temperature can then freeze faster than a larger volume of cold water that never evaporated at all.