FromCase Study: Tulsa, Okla., Loft Townhomes The 5 5/8-inch SIPs that make up the walls have an R-factor of 26 at 25 degrees F, according to USA SIPs. Between the SIPs and the cedar and Corten steel cladding materials is a rainscreen system from VaproShield of two breathable, waterproof membranes and brackets that hold the exterior materials away from the walls. USA SIPs: 800.835.3434. VaproShield: 866.731.7663.