The Yonex PolyTour Drive 16L Tennis String (Reel) is for baseliners with medium-to-fast swing speeds looking for a shaped string (8-sided) that grabs onto the ball for the ultimate spin experience. Yonex SIF technology infuses a silicon oil with the monofilament material during the manufacturing process. The technology vastly improves the string`s snapback and the effect lasts much longer than a simple coating.