Soap bubbles on a cubic frame. Bubble films always attempt to occupy the minimum surface area when stretched between two lines, and they meet other films at straight lines. This frame contained the minimum surface area configuration, but a bubble was blown into the centre of it. The internal pressure of this bubble attempts to force it into a spherical shape, but tension from the frame bubbles attempts to make it a cube. The balance of these two forces determine its geometry, which is a combination of the two extremes: a cube with curved sides.