The gas used in balloons due to its low density is helium. Helium is an inert, non-flammable gas that is lighter than air, making it ideal for inflating balloons that float. It is often preferred over hydrogen because it is safe; hydrogen is flammable and poses a risk of explosion. Helium is also abundantly available from natural sources, primarily obtained through the extraction from natural gas fields. Its unique properties, such as being odorless and having low density, make it suitable for a variety of applications beyond balloons, including in scientific research and medical technologies.