AlphaProTector™-SUL is a strong, secure, smart alternative to conventional roof felt underlayment. AlphaProTector™-SUL provides a synthetic solution to conventional roofing problems typically found with felt. Constructed of a high-strength, woven fabric and coated on both sides with a specially formulated anti-slip walking surface, AlphaProTector™-SUL is seven times lighter and 20 times stronger than 30# felt.