Helium leakage

Finally I received the GM862-GPS evaluation kit (it was retained for few days in tolls). I have had some problems with the USB-RS232 adapter I bought before I received the package (reading some forums I realised that those adapters hardly work), so while I find a computer with an integrated serial port I’ve been struggling with another problem I didn’t even know it existed.

It seems that in common (well, actually in ALL) balloons helium leaks in a relatively short time. That’s a known fact in toy balloons, but I though the knot was the responsible. I could read that actually helium passes through the rubber of the balloon, no matter if the material is latex (the common coloured balloons that can be filled with either air or water) or foil (in this case the balloon lasts more time to deflate, but it still does in few days).

So the problem is bigger than it seemed at first glance, since or the balloon must land to be re-inflated with helium (which by the way is not especially cheap, about 2500 € per cubic meter) or another way to stop helium leakage must be developed.
Many chemicals companies have developed different materials (with different prices) that claim to retain helium more time. But that idea does not convince me. Or the materials needed are not affordable by a common user or if they are they will need specialized operators for labours such cutting and gluing and related substances (like adhesives). In short, that will imply strong relations with the industry of chemicals and a budget I don’t have.

I've been thinking in a low-cost, home made and light material that can be used in this circumstance. The idea is to keep an extremely thin layer of oil (or any other fluid, preferable less dense than water trapped inside two layers of latex (of toy balloons, for example), and check if that fluid layer can somehow prevent the leakage of the air inside.
If that worked, its density will depend on the thickness of the fluid layer, but anyway it would be much lower than the one of foil, about 30 gr/m2 (to give some numbers, paper density=80 gr/m2; foil=200 gr/m2), for a fluid thickness of 0.01 mm. and a density of 1000 kg/m3 and two plastic layers of 100 gr/m3 density and 0.1 mm thickness.