Along the same lines as an earlier post about helium and materials that wouldn't allow it to permeate it, I wondered if a helium balloon with a fill tube would actually need to be sealed. What I mean is, imagine a balloon that has been filled with a 20'-30' very thin tube that is still attached to the balloon, trailing below it. There are at least the forces of pressure on the balloon itself, and the helium density against the surrounding air pressure to create lift, but I wonder whether such a balloon & fill tube assembly would need to be sealed, or even sealed well, at the base of the tube (lowermost portion). In the larger scope, I'll be filling a helium balloon of relatively small dimensions (less than 6' dia.), tethered to as much as 30' of very thin tubing (think fish-tank size or thinner). I'll be filling it through said tube at the time of deployment, and I've been wondering how to design the components that will keep the helium gas in the balloon & fill tube. So will the gas escape out the bottom of the hanging fill tube? Will there be too little pressure on the helium throughout to push the lighter than air gas out the bottom? If there is a condition that the gas would escape, and then with different dimensions it would not, then I could construct experiments accordingly. Ultimately, I'd like to cut down on weight, so even down-sizing components to avoid over-engineering would be significant.