On a whim I decided to make a lighter than air airship. An airship that could lift itself and a Lego man.
Using Excel I worked out the pattern of each panel that would need to be cut and then lofted this onto aluminised mylar film (one of the few materials that is lightweight and slows the leakage of Helium atoms). T he aluminised mylar film was originally invented to form an umbrella-like shield to disguise separating ICBM warheads from radar. I think its most common use these days is for reflecting light whilst growing cannabis indoors (so I am informed).
The panels were joined with Sellotape, allowing a slight overlap. The airship was filled from a container intended for the filling of party balloons. A piece of string helped control it.
I actually felt quite guilty about wasting the Helium. It has all been captured from oil-wells, mines, etc., where it has been for millennia. Once in the atmosphere the atoms slowly escape and dissipate into space.