Originally Posted by Forest Grump
Reflecting is one method but there are other methods of dealing with heat energy such as chemical reactions and adsorption.
From my perspective, on a practical basis there will be a combination of three things that will happen. Solar energy can pass through film, be absorbed at film, or be reflected by film. While solar energy can theoretically cause a chemical reaction, or can be partially converted to electricity, I don't see how that's going to apply here on a steady-state basis.
The more energy is reflected towards outside of vehicle, the cooler the inside should stay. Partial absorption at film will become heat which will warm glass enough to then transfer the heat to inside and outside air (a combination depending on relative temperatures and heat transfer rates). The worst case scenario is energy passing through glass and film, and being absorbed by surfaces inside motorhome. In that case nearly 100% of solar energy will have to be removed by air conditioner.
I'd like to learn if I'm missing how this film works. As stated before, up to 60 percent total rejection (upper limit reported by 3M) is pretty good. If I was going to keep my van for a couple of years, I'd try the film on a side window to test it. Reducing solar heat by +/- 50% would be great.