I am planning to replace my composition shingles with metal roofing. I remember hearing of a new product that is a sort of plastic waffle that is laid between the metal and the roof surface (wood plus felt etc). This creates a convective system that draws air under the metal and partially insulates the roof itself. I remember hearing that is was dveloped by a dentist or doctor and is equivalent to quite a bit of interior insulation. It may have been featured on "This New House" but I can't find any reference to it. Does anyone on this forum know about this product. Thanks