Material for making a model airship

Hi,

My uni group is planning to make a model airship (standard ellipsoid, about 18-20 feet in length), to be filled by hydrogen gas.

Researching on the net, I found that 'metallised nylon' is best suited for the envelope material. Can anyone guide me whether a better material is available?

And where can I buy metallised nylon for Airships from, and what is the approximate cost of metallised nylon or other suitable material?

We tried about with PVC sheets, but the gas retention is not pretty good.

Any help will be appreciated.

Thanks,

Mylar is strong, light, and is used to make helium balloons. Welding it is a little tricky as I learned making radiation sources for positron experiments a few years ago, but you might find a glue that would work