Bubble Rainbows: Why Are Clear Bubbles Colorful?

A bubble has two thin 'walls'—an outer layer and an inner layer made of soap molecules. When light hits the bubble, some bounces off the outside immediately, and some travels through the soap film and bounces off the inside layer. These two light waves then race back to your eyes at the same time.

Because the walls are so thin, the racing light waves 'bump' into each other. This is called interference. They get tangled up, canceling out some colors and making others much brighter. It's a microscopic light show happening on a surface thinner than a piece of tissue paper.

As the water inside the bubble moves around due to gravity or wind, the thickness of the bubble's skin changes constantly. Because different thicknesses create different colors, the rainbows appear to swirl and shift. When you see a bubble turn gold or dark, it usually means the walls are getting so thin they are about to pop!