Tecnifibre 4S 12m

The square section of 4S grips the ball with its edges, and the faster the swing, the more it spins. That gives the shots this string is bought for: deep topspin and short, sharp crosscourt angles. Co-polyester brings control and durability. Thermocore, a heating and cooling treatment during stretching, takes out some of the stiffness: ordinary polyester is harder on the arm. Tecnifibre suggests 22-25 kg and no more than 32 kg.