What Is a Bubble?

A bubble is a thin film of soapy water wrapped around a pocket of air. The film is incredibly thin, only a few millionths of a meter thick! That is thinner than a human hair.

Pure water cannot make bubbles by itself. Water molecules are too attracted to each other (this attraction is called surface tension). They would rather pull together into a droplet than stretch out into a thin film.

Soap changes everything! Soap molecules reduce surface tension, allowing water to stretch into a thin, flexible film. That is why you need soap to make bubbles. The soap molecules position themselves between the water molecules, allowing the film to stretch without breaking.