Tennis strings: Yonex POLY TOUR REV with a diameter of 1.30 mm is designed for its durability, especially for players who play aggressively from the baseline and prefer a spin game. The SIF (Silicone Oil Infused Filament) technology has silicone oils that are incorporated deep into the string's polymers. This reduces the mutual friction and ensures a higher snapback speed, increased power and, above all, a better spin game.