I recently put a radiant barrier in my attic. I looked at all of them and came to believe there is a lot of marketing gimmicks to the different products. Seems like they all try to make their product a little different and then say it's the best. If you've ever put tin foil in your window, you'll know the idea works. I ended up just getting the reflectix at lowes. http://www.lowes.com/pd_219377-56291...iant&facetInfo
I put it up and then have also read reviews that you want to install a gable fan in your attic as well to get the heat out. I put the gable fan in and set the thermostat to 105 as recommended by the manual, but it wont come on unless i set it down into the 90s. It's been getting to about 100 degrees outside here and I still dont hear my fan coming on.
When you install it, they say to leave a few inches at the top open and a few inches at the bottom (by the soffit). I pointed an IR thermometer on the bottom side of the foil and measured about 90 degrees. I put it on the bottom side of the exposed roof and measured 120 degrees. I was about 3ft away doing this test.
I called reflectix and they said I needed the product which had the bubble rap between two layers of foil, but that was more expensive and I couldn't figure why that was needed. So called again and asked why I couldn't use the regular (cheaper) foil material, and they said I could and it would be the same in that application.
So I would say i'm pleased with the way it seems to work in my attic, but I'm not too sure you really need to install it somewhere that doesn't have the sun shining directly on it. I really only installed it on half my roof which gets pretty much all of the sun exposure. I'm not too sure how it would be effective in winter months in keeping heat in which i guess would be more of your need.