Crinkle wrinkle

A thin film wrinkles differently depending on its thickness and elasticity—just as a prune forms wider, deeper wrinkles the thicker or less flexible its skin is.

In this image, a droplet of water rests on a polystyrene film a quarter of a micron thick, itself floating on water. Surface tension pulling the droplet into a roughly hemispherical shape also creates an inward pull on the film.