Tecnifibre X-One Biphase - String Reel Gauge:17 All Penn QST products are

All Penn QST products are USTA and ITF approved and endorsed by the PTR

The addition of polyester fibers adds stiffness

Meets USTA requirements for official size (41'9" x 3'6")

The Nike Primier Tennis Head Tie or bandana is made with soft fabric that helps pull sweat away from the skin for comfort during practice and play

Head's new Rave eyewear is stylish and lightweight for ultimate comfort and protection

Tecnifibre X-One Biphase - String Reel Gauge:17 All Penn QST products areAccording to Tecnifibre, the X One Biphase string uses High Heat Capacity (H2C) fibers, which allows the use of an innovative chemical treatment process called Trimerization. This new process increases the cohesion between chemical molecule links through extreme variations in temperature to result in ultimate dynamic efficiency (power) and exceptional feel. The new patented Biphasic process, with its visible marks on the string, extends string life by