are wrapped around the core fig1 also explains the good spun like effect of these threads occurring through the longer separated fibrils of the sheath group which produces an appearance similar to that of natural fibers and a material which is pleasant to the touch the use of coarser fibrils allows a satisfactory behavior of these threads in the further processing while retaining this good effect fig1 also shows that the fibrils of the sheath group are longer than the fibrils of the core group whereby the relative difference in length between core and sheath can be used as a measure of the spun like effect normally this difference in length is between 5 and 25 the apparatus in fig2 makes it possible to produce the filament yarns according to the invention in a co spinning procedure with two filament groups of different cross sections forming the sheath group two different polymers b and c are supplied in a molten state through separate intakes 6 and 7 of a common spinning nozzle pack 8 this pack of spinning nozzles has small and as an example two larger bores for spinning of polymer c as well as other bores for the spinning of polymer b thin individual threads 9 and thick individual threads 10 of polymer c exit from the spinning nozzle combining to form the sheath group and there also emerge the individual threads 11 of polymer.