The diffusion coefficients are 1 for air, and 3.7947 for hydrogen.
A more recent review is on the answer about https://www.quora.com/Is-it-possible-to-create-a-toy-helium-balloon-that-will-remain-aloft-for-years : “Not only does helium leak right through the skin of the balloon but regular air also leaks in.”
This matches the phenomenon of endosmosis such as linked above, and also the related experiment: