Here's Ray Harlan's site.
Click on "Materials" button
from homepage. Then look at "Ultrafilm".
Superultrafilm is probably too fragile for what you
want, but Ultrafilm may be worth getting, I don't know.
Ultrafilm is transparent, colorless. Anything having
natural refraction colors is probably too fragile for
anything over 8 grams. Anyhow, lists the weights of
both films. Thickness wise, Ultrafilm is 1.2 micron.
The next heavier film I know of is 2 micron film Mylar
sold by Mike Woodhouse, Free Flight Supplies UK. . The
next heavier is 5 micron, sold by same guy. BTW, 5
micron is the same as 1/4 MIL. His website,
http://www.freeflightsupplies.co.uk/
To find films, first click on "Indoor" button on
left of homepage. Then scroll down to find "lightweight
coverings" and click there.