The maker of Thermal-Pro says this is the first fabricated insulated steel siding product. Combining durability and energy efficiency, the panels are made from 29-gauge galvanized steel with a 4-mil-thick PVC finish and expanded polystyrene. With R-values ranging from 2.20 to 2.63, the foam is designed to allow water vapor to escape and its closed-cell structure resists heat loss through wood framing.
(From the October 2011 Edition of Builder Magazine)