Back in high school, I played around with microfilm on indoor models. Lightly thinned Aerogloss dope, a drop of glycerine or castor, I forget which, poured over a water surface, like a bathtub of water. Let you build things like a 39" span indoor rubber Free Flight planes, 8" or 9" chord, with a total weight under 10 grams (< 1/3 ounce?). Or a couple fly powered indoor models like the Bill Winter article in an old late 50s Flying Models magazine. Dope heavier than plastic film?

Last time I talked with the late Gerry Skrjnc of Micro-X models, he gave me a couple square feet of a plastic film that was supposed to be slightly lighter than that microfilm. At the time, I was proud of an 8 gram E-Z Bee from one of his kits. Then he showed me his, same kit, 4.5 grams.

As far as the relative weight of Silk/Dope or Tissue/dope, that will depend on the amount of dope applied, how much thinning, how much sanding/polishing, and even, like the chart shows with Mono, how much of what color dope is used. Most free flighters I know still prefer to use a colored tissue or silk with just enough clear sanded dope to seal the weave of the material.

Still don't think I've ever seen a mirror finish with film like I've seen with fabric/dope.