Abstract: A monofilament string for use in string racket sports, wherein the monofilament string comprises: a covering material; a core material embedded in the covering material, wherein the core material comprises: a sea region comprising a thermoplastic elastomer; and a plurality of island regions comprising a thermoplastic plastic doped with one or more doping agents, wherein the plurality of island regions is embedded in the sea region; and wherein a geometry and/or a distribution of the island regions in the sea region is such that a tangent modulus of a stress-strain curve of the monofilament string increases with increasing strain in a playing stress range.