I believe I know the answer to this question; I need an expert to verify it for me. I work for a company that makes latex balloons. The people that have been here for a long time insist that if one is putting a small (5" balloon) filled with helium inside a larger (30") balloon then one must fill the larger balloon with helium as well. I've asked why (repeatedly) and get specious arguments that the small balloons don't "leak" as much with helium on "both sides" of the membrane; some go so far as to say that (somehow) the helium in the larger balloon is going into the smaller balloons (I walk away from that one). I think this to be nonsense and in fact a tremendous waste of helium. I would go further and say that in fact all that you are doing is making sure that the larger balloon "leaks" as well, and will deflate at a much faster rate than if it was filled with air. I want to be certain that in fact the larger balloon should be inflated with air. A postulation that I make, which may in fact not be very accurate, is that the pores in the smaller balloon, with helium "pushing outwards" would have larger molecules (mostly nitrogen) "pushing back" and blocking the pores. In my minds eye I can see this, but have no basis for it being close to fact. Thanks for any input.