Why water drops last longer on a hotter pan: the Leidenfrost effect

Flick water onto a warm pan and it sizzles away in a second. Make the pan hotter, past about 193 °C, and something odd happens: the drop pulls into a bead, skates around silently and can survive for over a minute.

This is the Leidenfrost effect. The underside of the drop flashes to steam before it can touch the metal, and the drop ends up hovering on a cushion of its own vapour about a tenth of a millimetre thick. Steam is a poor conductor of heat, so the cushion also works as insulation.

In one classic measurement, a drop that vanished almost instantly at 168 °C lasted 152 seconds at 202 °C.