Normally, they are sphereical due to surface tension but Tom Noddy , "Bubble Guy", is able to blow 'cubic' bubbles.
Check out Ron's Bubble page for more on bubbles.

Area Sign - Mixing Waves Bubble Graphics Board Bubble Suspension Bubble Tray Cells Resonant Bubble Soap Bubbles Soap Film Painting

Color Complementary Color Mixing Color Separation Interference Surface Tension

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