Hi-tech spiral steel core strings. This core has a greater elasticity than conventional strings, which means less inertia and a longer period of musical vibration. The sound is full and homogoneous, balanced and voluminous. Equally effective playing arco or pizzicato. Spirocore"s hi-tech core makes for effortless fingering, responsive bowing, stable tuning and a very long string life. Thomastik Spirocore Cello D String, Chromesteel wound on steel core