Helium is the gas commonly used to fill balloons. It is lighter than air and will cause a filled balloon to rise. Unlike hydrogen, which is also a lighter-than-air gas, helium is non-flammable and much safer to use. Helium balloons are often popular for celebrations, parties, and decorations, providing an element of fun and visual appeal. Additionally, helium is an inert gas, meaning it does not react chemically with other substances. Its unique properties make it ideal for both commercial and recreational balloon use.