[ifuller]

Does anyone know where I can buy a balloon, such as a normal birthday balloon, that is designed to be filled with hydrogen gas? I know that I can fill a regular balloon with hydrogen but the gas diffuses so rapidly that it really isn't useful. Does anyone know if a balloon normally used for helium will work? Thanks

[JCKnowledge]

Ordinary balloons are formed from liquid rubber (latex).  Helium balloons are a form of metalized or "foil" nylon, not Mylar (boPET) as people often mistakenly call them.

Based on atomic size, I would surmise that the larger H₂ molecule would effuse at a slower rate than the smaller He atoms.  The issue of air densities could pose a problem for the structural integrity of your balloon, but the difference between H₂ and He should be negligible (for what you are trying to accomplish).

To specifically answer your questions, yes, a balloon normally used for He should work, and your local party supply store should sell "Helium" balloons - though they don't necessarily have to read 'Happy Birthday', I would, however, keep the birthday candles away from them.

I hope this information was helpful...

[Borek]

Note: just comparing sizes and molar masses can be misguiding. CO₂ molecules, while larger and heavier, penetrate many types of tyre rubber much faster than oxygen and nitrogen. That's not to say you are wrong, just to warn

[Arkcon]

I always figured, for ordinary balloons, most gas diffusion occurred at the tied off knot, and the loss through the "skin" was negligible, at least by comparison.  Dunno what happens to a really taught, filled balloon, with the the knot pinched off and melted shut, but yeah, the metalized foil ones used for He should hold H2 as well, or better.

[ifuller]

Thanks a lot everyone for the info.

And JCKnowledge,
I am actually trying to use a balloon as a type of diaphragm to even out the flow and pressure of hydrogen through a system.

[Arkcon]

Interesting application.  So, maybe you want not a balloon, but a semi-rigid reservoir, as a pulse dampener?  For maybe a GC-type application? That could be much thicker, and if the flow is fast enough, diffusion through such a wall would be negligible, maybe.