Absolutely, A foil backing is a separate layer that can and does reflect the heat back. Kool Ply will and does work. But it only works because it has a separate, smooth, reflective surface with which to reflect the heat with. A painted on layer on the bottom of the plywood will do next to nothing since the reflective layer is almost non existent - it has soaked into the rough surface of the plywood. Go back to the original question. It was about painting on a reflective surface to reflect the heat back out. All I'm saying is that the surface must be smooth and polished. Also, I think all Jay J is trying to say is the building materials a true reflective layer will be hotter than they were without the reflective layer.