In article Larry Dighera writes:
On Tue, 4 Mar 2008 14:47:54 -0800 (PST), Ricky
wrote in
:

hydrogen is a stronger lifting gas than helium.

The atmospheric displacement of hydrogen (H2 MW=2), with one fourth
the molecular weight of helium (He2 MW=8), should be a considerably
larger percentage of its mass. But because the hydrogen molecule is
physically smaller, containing it within the balloon envelope may be
an issue.

But, the hydrogen molecule is 2 hydrogen atoms, at some distance.
The helium molecule is 1 helium atom, so it is smaller. As I recall,
helium leaks more.

However, from reports, hydrogen tends to ignite rather easily.

Alan