Would your kids want to try this amazing bubble cube trick? Sign up for our FREE email newsletter to get more kid-friendly experiments and activities delivered to your inbox. Have you ever wondered why bubbles are round? When you blow a bubble, you’re stretching out the bubble solution. However, the soap doesn’t want to be stretched so it will try to make itself as small as possible. The smallest surface a bubble can create while keeping the same amount of air inside is in the shape of a sphere.