Soap bubbles on a triangular prism frame. Bubble films always attempt to occupy the minimum surface area when stretched between two lines, and they meet other films at straight lines. In this frame, three bubbles were blown into a frame in which the minimum surface area was attained. The presence of these bubbles has distorted its shape. Each end of the prism has a truncated tetrahedron, capped with a central triangular prism joining the two. The internal pressure of each bubble attempts to force it into a spherical shape, but tension from the frame bubbles tries to make them tetrahedral. The balance of forces leads to a combination of the two extremes, giving the bubbles curved sides.