I would have to agree with the Mr. Clean pads. The best way would be to paint over it only if you have the same flat paint...but I know sometimes it gets lost or dries out. So the eraser pad should do ... read more
Foil backed plywood is the more efficient than spray. Here is one site but many use the same figures. http://www.atticfoil.com/install-questions/paint-vs-foil.html