I've never heard of a radiant barrier paint.

I work as a delivery driver for a building products wholesaler specializing in plywood and similar products.

We sell several different brands of radiant barrier covered OSB. It's known by several different names but it's basically a piece of OSB with a layer of thin mylar film applied to one side.

Builders are using on the roof and on the walls of new homes and when they reroof existing homes.

From everything I've heard it can greatly reduce your energy usage, reflected energy of the sun and all that good stuff.

I'll do some hands on research when I go to work Monday and ask around to see if anyone has heard of any specific brands that are any good.
Will report back with my findings.