Tourna Premium Poly is made of advanced co-poly materials which make it extremely durable yet softer than many traditional polyester strings. Great for hitting huge topspin. The materals are very much like expensive polys. Tourna has been making award winning tennis strings for over 12 years. Tourna is known for Tourna Grip, the iconic Blue Grip that can be found on hundreds of touring pro's racquets. Trust your game to a company that has been making game changing tennis accessories for over 48 years.