Dow. SIS Structural Insulated Sheathing combines a moisture-resistant blue foil outside face, a polyisocyanurate foam core, and structural sheathing. Builders can use ½-inch (R-3) panels to sheathe entire exteriors or 1-inch-thick (R-5.5) 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.