The answer is a Bubble.
As you know, a bubble is a threadlike film of soapy water. The majority of the bubbles that you see are filled with air, however you can create a bubble using other gases, such as carbon dioxide. No matter what shape a bubble has originally, it will try to become a sphere. The sphere is the shape that reduces the surface area of the structure, which makes it the shape that requires the least energy to achieve.
Of interest, if you want to make giant glowing bubbles just click here to find ingredients and instructions. Enjoy!