Yonex REXIS SPEED Tennis String is designed to play slightly firmer than REXIS COMFORT. Because of this, REXIS SPEED is a crisp playing multifilament string that will hold up well in a hybrid with a polyester string. A flexible material called FORTIMO fills in the gaps in the multifilament structure, and helps increase durability over a standard multifilament.Construction: Multifilament with FORTIMOColor: WhiteGauge: 16L / 1.25 mm | 16 G / 1.30 mmLength: 39 ft