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If you got really hot steam in there, there'd be at least some lifting force as H2O only weighs ~18 amu whereas N2 weighs ~ 28 amu and O2 weighs ~ 32 amu. But it would work better on Venus with its mostly CO2 (~44 amu) atmosphere

Hot water balloon. Hot earth balloon. Hot fire balloon. Hot air balloon. Long ago, the four hot balloons lived together in harmony. Then, everything changed when the hot fire balloon caught on fire. I don't know what we were all expecting to be honest. That's what it does.

With a diving suit and suitable burners you could attempt the first transatlantic subaquatic hot water balloon flight. You'd need people to keep resupplying your oxygen tanks or old style diving suits a long oxygen pipe and a boat with an air pump.

Not saying I'm speaking from an actual 70's experience, but never have more than six people on a waterbed; eight is too many. There's a "wave effect" that keeps escalating, and it's embarrassing when you and a young lady get flipped off the side of the bed.

Don't they jump on those things in the desert? I'm pretty sure I saw some troops bouncing around on one of those things during Desert Storm. Actually looked like fun.