Yonex Rexis Comfort tennis string for players of all swing speeds looking for a soft string with added comfort. 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.