As a co-polyester monofilament, Yonex PolyTour REV will give you the needed control to execute your most powerful hits. Packed with 8 sides, PolyTour REV not only puts a tight grip on the ball, it also features SIF technology (Silicone Oil Infusion), which helps the strings snapback powerfully during impact for extra ball rotation. This co-polyester also has above average comfort for a poly-based string, making it an obvious choice for any player who wants a more arm-friendly control string.