While it is possible to create a wide variety of baloon shapes, it's impossible to achieve straight lines due to the effects of air pressure on the materials used.
The proposal here is to use styrofoam or another light, but heat insulating substance and to create such arbitrary shapes.
Now I can have that floating castle that looks like a floating castle
Thanks, Vernon-- theircompetitor, Mar 29 2006 I foat yes!-- bungston, Mar 29 2006 I don't see any real problem with this, I wonder why no one has done it yet?-- wagster, Mar 29 2006 My suspicion [wagster] is that the geometry can play a negative role (i.e. an upside down boat does sink) , however, I would still think it's possible to overcome those issues given a light enough/hot enough gas.
Oh, and thanks [bungston], I was typing this on a PDA in transit.-- theircompetitor, Mar 29 2006 I liked it the way it was. It had a certain charm.-- bungston, Mar 29 2006 //thanks vernon\\? better hope he doesn't annotate...-- zeno, Mar 29 2006 If large enough and with proper ballast, I can imagine riding on top of the castle, on a fortified spot, of course.-- Shz, Mar 30 2006 random, halfbakery