I was reading an article in this month's "Flying Models" about using balloons for pressurized, collapsable fuel cells. The article was mostly aimed at the smaller 1/2A size engines, but I was thinking it might work on larger ones as well. The question I have is wouldn't the balloons eventually lose their elasticity? The whole thing was about keeping constant fuel flow without having to rely on the exhaust or gravity. I'm sure they make them, but on something that small, I would think a pump would be a waste of space and weight. Does anyone make a collapsable, self pressurizing fuel cell for larger planes? If so, what are they made of, and how long do they last?