make a list
Bike tire inner tube
ive seen a few designs that used pantyhose.
Any rubberised (= high friction and non-conductive) material will work.I used to use a VdG with a ragged old belt held together with staples and wishes, and it worked fine.For a small generator, large rubber bands will work.I would be tempted to try cutting a strip from an old neoprene wetsuit or rubberised macintosh (the coat, not the computer).If you were feeling really creative, you could even try weaving a belt from ordinary rubber bands.
It's like a big rubberband but a bit papery
The big ones, I believe, just used standard conveyor-belt material (rubberized fabric). If you want to check that, contact the Boston Science Museum, which owns one of research machines built by Van de Graff himself (and used as an early "atom smasher"; one tube was the generator and the other was the experimental column). Actually, they might be good people to contact for more specific advice on this topic.
There's also the lazy solution: Look at the catalogs/companies which sell hobbyist VdG generators and see if they sell spare belts.
Just buy one of the proper width, We tried to make one but when I started it up it lasted all of 2 seconds.
If you do try it's got to be: taught, flexible, strong and able to produce static.