the rutil type which pigments are insoluble in the polymeric material the tenacity of the yarn may be about 70 85 cn tex and the elongation at rupture of 7 to 15 application_number US 33970682 A description in fig1 the numerals 1 and 2 refer to parts of two spinnerets the two plates are spaced from each other and arranged in parallel in a melt spinning assembly between the plates 1 and 2 and above the plate 2 are two chambers 3 and 4 respectively which are connected to two feed lines for two spinning liquids not shown through the spinneret 2 runs channels 5 which end in the chamber 3 at a point opposite channels 6 provided in the spinneret 1 the channels 6 converge at their outlet ends at the lower side of the plate 1 spinning liquid flowing through the channel 6 is cooled in the ambient air below the spinneret 1 to form filaments which are subsequently drawn off and wound in a known manner into the chamber 3 there is forced the sheath polymer for instance a nylon 6 melt and into the chamber 4 a melt of the core polymer for instance of polyethylene terephthalate containing 0 6 by weight of carbon particles in this process the polyethylene terephthalate is extruded through the channels 5 in the direction of the channels 6 to which also the nylon 6 melt is displaced through the channel 6 there will consequently be a downward flow of a skin or sheath of nylon 6 containing a core of polyethylene terephthalate thus the filaments formed therefrom have a skin of nylon 6 and a black core of polyethylene terephthalate at the outlet openings.