YONEX Poly Tour Rev Tennis String is designed for baseliners with medium-to-fast swing speeds looking for a shaped string that grabs the ball for the ultimate spin experience. The Silicone oil Infused Filament (SIF) technologymonofilament infused with Silicone oilallows big hitters to experience ultimate spin from intense snapback speeds. Greater snapback produces a powerful spin. SIF Technology with unique pentagonal structure allows the string to move faster than conventional models, increasing spin.