[EricH]

Of course, I didn't specify how much extra you pressurize it. The kind of pressures I'm used to dealing with for air/helium, you can't measure them in PSI unless you really like small decimals.

I'd also note that at least one maker of the size of helium balloons that can possibly lift an FRC robot does specify that they be pressurized, and goes to great lengths to have the balloons maintain that pressure. This is partially because said balloons need to maintain a given shape, granted--but you have to wonder if it doesn't give a tad bit of extra lift.

(Then again, these helium balloons can weigh several hundred pounds empty.)