Grade 1 "Superia Pro" classical guitar strings from Rotosound are manufactured to a high-tension characteristic specifically designed for fingerstyle playing. The wound strings are silver-plated copper on a nylon core and the plain strings are high-quality rectified nylon. Ball end.NRH 1, 2, 3 High quality rectified nylon NRH 4, 5, 6 Silver plated copper/nylon core