Dow SIS Insulated Structural Sheathing Insulation and structure have been at odds in high-performance homes for years, giving pros the challenge of providing strength and efficiency while minimizing cost and extra labor. Dow’s Styrofoam SIS panel combines both functions in a structural foam sandwich that eliminates the need for bracing or shearwall panels on projects using foam exterior sheathing to beef up R-values. Three layers are pressure-laminated to produce the SIS panels in ½- (R-3) and 1-inch (R-5.5) thicknesses: a moisture-resistant blue foil outside face, polyisocyanurate foam core, and structural sheet. Builders can use ½-inch panels to sheathe entire exteriors or the 1-inch-thick panels as shear panels on corners to match up with 1-inch foam sheathing on the rest of the exterior. Joints between panels are sealed with Weathermate tape. SIS panels contain 80% post-consumer recycled content and are Energy Star rated. 866.583.2583.