The SL series uses the "Muscle Tec" string system, to enlarge the power zone of the racket by allowing the strings to move over a smooth rounded surface rather than being static as in conventional rackets. "Muscle Tec" enables the strings to be strung at a lower tension yet still gives a high tension feel. It also uses Nano Technology and Nano Superlight Resin. SL 70 Specification:*70 Grams Frame Weight *95% Nano Graphite - 5% Mg *Hi Flex Precision Shaft and High Flex Top Cap *Double Grommet at Tee Joint *Constant Taper Frame 10-10. 7mm *Head Loop takes 30LBS-13. 63 KG *Nano Tec and Nano Superlight Resin *Two Piece Construction *Full Racket Cover