See Installation Photos - Click Here 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 Comp, Sharkskin Ultra and Sharkskin Ultra SA have received TDI approval. Here is an example below of two buildings being reroofed in the same city at the same time. One using standard felt and the other using Sharkskin Ultra. This is how they looked after the last storm came through. Which would you use? The Sharkskin Ultra clearly held up and is the best choice.