A mold insert has at least one filament cavity and a stack of at least a first and second insert plates, wherein the first plate has a front face that closely abuts a front face of the second insert plate. A portion of the a filament cavity is provided in at least one of the front faces of the first and second insert plates such that the filament cavity is open at a top surface of the mold insert but does not extend to a bottom surface of the mold insert. A venting cavity is provided in the same front face of the insert plate in which the portion of the at least one filament cavity is provided. The venting cavity, which is in air-conducting connection with the blind-hole end of the filament cavity, has a depth between 1 μm and 20 μm. A method of manufacturing the mold insert includes providing first and second insert plates, forming a portion of a filament cavity into at least one of the front faces of the insert plates, forming a venting cavity into the front face with the filament cavity, and bringing the front faces of the plates into close abutment to form a filament cavity.