Yonex aerobat boost is a hybrid mix between two types of strings, Mains core- high intensity nylon multifilament super fibre Vectran . Mains outer wrap - high polymer braided nylon fibre, oval shaped.Coating - Polyurethane tacky feel. Crosses, core - high intensity nylon multifilament, outer wrap - high polymer nylon fibre. Hard feeling for great control, power and hitting sound. Mains in Yellow colour, Crosses in dark Grey colour. Only single sets available, mix of 18ft Mains and 16ft Crosses for £8.00. Reel of 660ft in Yellow and dark Grey £120.00. Made in Japan.