Progressive Foam Technologies, Inc. makes contoured foam underlayment under the brand name "Thermowall". The material is shaped to precisely fit behind nearly any manufacturer's siding profile sold in the United States. Installed over exterior walls just before placement of the siding, the underlayment provides a continuous solid backing that helps vinyl siding resist impacts that might otherwise cause cracks or dents. By adding an additional foam insulation layer, the R-values of exterior walls are increased by R-2.8 to 3.3, depending on the profile, not including the vinyl siding.
Crane Performance Siding uses a similar concept to create lines of solid-core siding products including Craneboard and Techwall Plus. These products fuse a contoured polystyrene backing material to a vinyl exterior facing for a solid insulated wall system with an overall R-rating of 4 to 4.5, depending on the product selected.
Both the foam underlayer and the solid core siding are made to fit most exteriors. Unlike conventional siding, the foam offers protection against dents and other impact damage, allowing the siding to remain aesthetically pleasing, functional, and lasting.
Please also see
fiber cement siding
Courtesy of PATH
www.pathnet.org/homeowners 
