The 4S string is the one that will generate the most spin in this range with a square construction that allows even more spin.Best tennis strings for professional players and your sports clubs. Tecnifibre is the leading brand in strings and offers a wide range of strings dedicated to all levels and requirements of players Guarantees the greatest flexibility for polyester monofilaments to generate less fatigue. Co-Polyester compound: Selection of polyester granules known for their specific flexibility. High quality material thanks to a mix of different polyesters.