I am asked all the time about insulation in attic spaces. There is no such thing as too much insulation, however, all insulation no matter the thickness will still not stop the radiant heat from penetrating down into the living spaces below.
In theory, if all of our homes were built under the shade of a tree, we wouldn’t need radiant barriers. Since that is not the case, Radiant Barrier Foil is the next best thing to naturally occurring shade. Simply put: radiant barriers reduce the amount of heat entering the home/building. Reducing the amount of heat gain helps to reduce the energy needed to remove the heat (air-conditioning) and makes the living space more comfortable.
Radiant barrier also improves the R-value of your insulation by reducing convective looping so your home stays warmer during the cold seasons.
I have personally installed this in my attic and have seen a dramatic difference in temperature decrease from floor to ceiling. Prior to installing this I used a Fluke thermal imaging camera Ti-10. The temp at the ceiling from the floor was 11 degrees. After installing this product I took the thermal imaging camera in the same spot in the ceiling with the same outside temp and humidity level as the first test reading. The results showed an 8 degree difference!
Here is the link to this product: http://www.atticfoil.com/index.php/diy-project-gallery/