Professor John Russo, Construction Engineering faculty member at Iowa State University in Ames, has served as a consultant on several cases involving the installation of wood siding over foam. We asked him to update us on the problem because he is one of the most knowledgeable and objective individuals in the U.S. concerning the issue. This report is based on Dr. Russo's three years of study and involvement. by John Russo Rigid plastic foam was developed in the 1930s as a flotation material, but it has found many other uses since. One recent and popular application is its use as an exterior sheathing material, primarily in the residential-construction market, because it provides good insulation at