Polyester. Pro Line No. II offers tournament players an extraordinary mixture of power, control and spin potential. A constant dynamic response off the string bed and the maintenance of the installed string tension grant steady playing characteristics and performances. Based on Kirschbaum’s 20 years of experience in string manufacturing of monofilament tennis strings made of co-polymer materials with top quality products like Competition and Touch Turbo, they continuously improve and develop new formulations. Outstanding combination of power and control. Highest spin-potential without string-slipping. Extreme durability and best tension-maintenance. Works great as a hybrid to meet your personal demands.