Sharkskin - The Ultimate Roof Underlayment. The Sharkskin line of products is designed to ensure that quality roof installations are not compromised by inferior underlayment products. The state of the art in underlayment is found in Sharkskin which is the only patented roof underlayment on the market (U.S patent #6,308,482). Sharkskin is 100% polypropylene which gives it the following advantages over competitive products and asphalt felts. Sharkskin Ultra and Sharkskin UltraSA are Poly Foam Approved. Sharkskin Ultra Radiant was developed to exceed California Energy Code Title 24 Standards.