Originally Posted by witoke
Wouldn't it work better on the outside?
In my experience covering windows from outside makes biggest difference when trying to keep van cool on a sunny day. Once solar energy goes through glass, it's hard to keep it from moving to inside of van unless the insulating panel is air tight. And if air tight the glass can get very hot. So much so I was concerned it would damage the adhesive used to secure glass to van body. Don't really know what temperature rating it has. Glass expansion also concerned me a little.
We have been using similar insulation cut out of 1/4 inch thick foam panels on door glass for over 5 years, and while they work great for hot and cold, it's outside curtains that reduce air conditioning load drastically when sun is shinning directly on glass. We made them out of white vinyl to match windshield and hang then off rain gutter. They are same color as van so they don't look too bad.
I agree with previous comment that outside curtains are a pain when trying to look outside. That's why we only use outside curtains to block direct sun when absolutely needed. Since we have an extended window van, I often leave some of the smaller outside curtains off so we can see out when needed.