Gil, the regular 9 inch party balloons work just fine, if you blow them up a couple times and stretch them a bit they work better. Be sure to get all the air out of the balloon when fueling. I can get a full pattern with one hooked to a norvel 061. Once they have been used, they should last at least a couple weeks, maybe a month before i replace them.

Gil,

As Ray said, get all the air out of the balloon while filling it. Like they do with injections, pull some fuel into the balloon, tip the bulb or syringe up so you can push out everything but the fuel, then add your fuel load.

A 9" party balloon sounds large to me for the volume even a NorVel .061 needs for a full pattern. A few test flights to make sure you know how much fuel to load - marked syringes are great for this and should serve you well.

And, the cautions about checking the condition of the balloon frequently, changing it as soon as there's any doubt is right on. Compared to commercial tanks, replacement of a slack balloon is cheap, and only a few minutes work to prepare.