As a final layer of protection, this high-performance underlayment covers the entire roof after the WinterGuard application. An asphalt-impregnated fiber-glass-reinforced organic felt underlayment designed for use on roof decks as a water-resistant layer beneath roofing shingles, Roofers' Select is more dimensionally stable than standard underlayment when wet. Its resistance to "hygro-expansion" significantly reduces the wrinkles that can result when the felt picks up moisture, thereby reducing the occurrence of visually objectionable wrinkles that can telegraph through to the shingles applied over it. Roofers' Select meets the underlayment requirements for the CertainTeed Integrity Roof System, which is comprised of underlayments, shingles, accessory products and ventilation all working together. The Integrity Roof System is designed to provide optimum performance-no matter how bad the weather conditions are.