The Yonex Rexis Feel tennis string is a high end multifilament string, offering the most power, comfort, and feel from the entire Yonex line of string. 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.