Helium is the second lightest gas (0.1786 g/L, 14% the density of air, at STP). For that reason, it is an attractive gas for lifting as well.

A major advantage is that this gas is noncombustible. But the use of helium has some disadvantages, too:
* The diffusion issue shared with hydrogen (though, as helium's molecular radius, 138pm, is smaller, it diffuses through more materials than hydrogen).
* Helium is expensive.
* Although abundant in the universe, helium is very scarce on Earth. The