just the humidity level in the gas used to fill a balloon is going to have a significant effect on its properties, human breath will have more c02 that air and s higher humidity. Any canned pressurised gas, will be pure with zero humidity. Heating exchange works through convection cells, the greater the number and the smaller they are, the lower covective heat transfer will happen, so filling a room with balloons, and you have made foam, and at that point the acoustical properties must be pronounced fun stuff The activity of silk working as a sound absorber is its property of bieng one of(the) best heat conductive substances, and as a basic fact, all sound is eventualy turned into heat The silk is presumably working to convert the mechanicsl motioninduced by sound into heat, quickly disapating it and releasing it to the air.