With 4S Tecnifibre gives big hitters a durable, low-powered co-poly with MASSIVE spin potential, impressive tension maintenance and great feel (especially for a firm monofilament). Boasting a square profile and sharp edges, this string puts a very tight grip on the ball. Topspin players will be able to hit high-arching, spin-loaded balls that come down sharply and explode off the court. For this string Tecnifibre uses Thermocore Technology, a multi-stage heating technique designed to soften the structure and reduce harsh impact vibrations. This helps explain why our playtesters were so impressed with the comfort level. Players looking for a durable co-poly with phenomenal control and spin-potential should definitely give this one a serious look.