[hammock]

So would a wall of helium balloons work as a sound dampener? Or perhaps diffuser? A lot cheaper than fiberboard & foam

[ParacelsusOfEgg]

I doubt it would be cheaper than foam, but this is similar to gas filled windows. Argon or Krypton gas is pumped in-between the window panes to provide another layer of insulation.

[hammock]

Makes sense