Why Do Soap Bubbles Have Rainbow Colours? The Science Behind the Shine

A soap bubble can look like a tiny floating planet, covered in shifting blues, greens, pinks and yellows. The colours appear, disappear and move across the surface as the bubble drifts through the air. Yet there is no coloured dye producing this spectacular effect. The secret lies in the extraordinary behaviour of light when it meets an incredibly thin film of soapy water. This phenomenon, called thin-film interference , is also responsible for colourful patterns seen in oil slicks and certain transparent materials.