HEAD Hawk Touch 17 1.25 With HEAD Hawk Touch 17 tennis string, youll experience maximum control and more touch. A unique multi-stage heating process features Crystal Core technology to deliver the highest possible energy efficiency for explosive power with optimized control in every shot.Endorsed by pro player Novak Djokovic.HEAD recommends lowering string tension by at least 10%. Technology Crystal Core: This newly developed, innovative process allows HEAD to control the molecular crystal structure within a monofilament string and engineer different material properties in the outer and the core region of the string, setting it apart from conventional monofilament polyester strings. Highly orientated molecules on the outside of the string generate stiffness and energy efficiency releasing more power and explosiveness. Meanwhile, a more crystalline inner core is adding dampening and touch to the strings performance.