The Yonex Resxis Speed tennis string offers a responsive and lively feel. For players of all swing speeds looking for a highly-responsive string with added speed. The REXIS string provides improved power, repulsion, and durability from the innovative FRF (Fusion of Resin Filament) production process. Upgraded at the molecular level for greater elasticity, the super-solid REXIS string structure is produced by filling the gaps of ordinary multifilament string with the new, more flexible material, FORTIMO™. FORTIMO™ is developed by Mitsui Chemicals, Inc. Resin is bonded to nylon filaments by plasma on a molecular level to improve repulsion and durability.