The gas most commonly used in balloons for decoration is helium. Helium is a colorless, odorless, and non-toxic gas that is lighter than air, allowing helium-filled balloons to float. It is often preferred over hydrogen for safety reasons; hydrogen is flammable, while helium is inert and poses no risk of combustion. Helium balloons are popular for parties, events, and celebrations, as they create a festive atmosphere. The gas is sourced from natural gas reserves, and while it is the second most abundant element in the universe, its availability on Earth is limited, raising concerns about its conservation.