> It will have the same outgassing problems. It will not. The outgassing is proportional with the difference in partial pressure. On the outer foil the differe

> It will have the same outgassing problems. It will not. The outgassing is proportional with the difference in partial pressure. On the outer foil the difference in partial pressure is 1 atmosphere (only helium inside, no helium outside). In time helium will leak out. Air will probably not leak in, by you can add it, to maintain equal pressure. The point is that you won't add a lot. Let's say that in one year 5% of the helium gets replaced. That means the difference in partial pressure on the inner foil is at most 0.05 atmospheres. The leakage will be much lower. Most likely you would not need to refill the helium inside the inner foil more than once during the lifetime of the airship.