When a soap bubble is blown, a pressurized bubble of air, which is contained within a thin, elastic surface of liquid, is created. Soap is generally used in such process since most liquids cannot maintain a stable surface tension to create a bubble.

When the bubble is blown, the surface film tends to contract causing an increase in the pressure inside the bubble. A soup bubble has two liquid-gas interfaces - the one on the inside of the bubble and the other on the outside of the bubble. In between the two surfaces is a thin film of water.