HEAD Synthetic Gut Reel 660' - YellowHEAD Synthetic Gut Reel 660' Yellow HEAD Synthetic Gut Tennis String features a solid core construction with an outer wrap. Compared with Synthetic Gut PPS (older version), HEAD Synthetic Gut is offers a more spin friendly response, as well as improved durability. This string offers good all around performance at a great price, and it works well as a hybrid with a polyester string. Colors: White, Black, Yellow, Blue Composition: Nylon Copolymer Core,