This. Also, even if aerogel tech improves drastically, there is another, more insidious problem. Small-molecule gases diffuse through solid matter (search for

This. Also, even if aerogel tech improves drastically, there is another, more insidious problem. Small-molecule gases diffuse through solid matter (search for "helium leak iphone" if you haven't read that fascinating story), so hydrogen will be slowly leaking out of aerogel, much like it does leak from a normal balloon. Air diffuse back inside at a much, much slower rate - with net effect that pressure inside drops. This will crush/crumple aerogel, with no easy "top it off" option available for normal balloons.