A bubble is made of transparent water enclosing transparent air. However the soap film is as thin as the visible light wavelength, resulting in interferences. This creates iridescence which, together with the bubble's spherical shape and fragility, contributes to its magical effect on children and adults alike. Each colour is the result of varying thicknesses of soap bubble film. Tom Noddy (who featured in the second episode of Marcus du Sautoy's "The Code") gave the analogy of looking at a contour map of the bubbles' surface. However, it has become a challenge to produce artificially coloured bubbles.