Soap Bubble Geometry Shapes: Science Experiment for Kids to do at home 

Explanation: Bubbles are like a very thin envelope of soap water surrounding a volume of air, Generally bubbles always takes spherical shape because sphere being the most stable shape, and also due to surface tension (which is an attracting force, that pulls the water molecules together, for ex: dew drops are always spherical in shape due to surface tension). Here, the addition of soap to water reduces its surface tension and helps it to be more stretchy. 

In this experiment when we dip the bubble frame into the soap solution, the solution is stretched to all the sides of the frame and soap solution sticks to the frame strands, and when we blow a bubble at the point where soap layers meet, we get a bubble of the same shape as that of the frame. You will also notice that the soap layers join in straight lines. 

Source: https://www.zlifeeducation.com/blog/bubble-geometry/