Droplets bouncing off surfaces are an everyday phenomenon, like raindrops bouncing off lotus leaves or water drops sizzling in a hot pan, levitating and sliding around—aka the Leidenfrost effect.

When a droplet of water falls on a hot pan, it dances across the surface, skimming on a thin layer of steam like a tiny hovercraft; this is known as the Leidenfrost effect. But now, researchers know ...