Filaments or bundles or slivers of filaments obtained by extruding a molten synthetic linear polymer are washed in a continuous operation, before effecting at least the major portion of a final cold-drawing treatment and while they are still unoriented to any significant degree, until their content of monomers, low polymers and foreign substances is lowered to a desired low limit, and thereafter the filaments are cold-drawn till they are completely oriented. The filaments may be washed, cold-drawn and dried in a continuous operation while they travel in a substantially helical path. The filaments may be subjected to a preliminary wetting before the washing treatment. They <PICT:0736524/IV (a)/1> <PICT:0736524/IV (a)/2> may also be given a low degree of stretching prior to washing. p The stretched and dried filaments may be continuously crimped and subsequently cut to short fibres. The synthetic linear polymer may be a polyamide, e.g. a polymer obtained by polycondensation of amino-caproic acid or caprolactam. The treatment may be carried out in apparatus comprising at least one pair of rotatable rollers, stationary in location and skewed with respect to each other, at least one of the rollers of a pair being driven so as to advance the filaments continuously in a helical path, means for feeding the filaments to the rollers prior to executing at least the major portion of their final cold-drawing, means for continuously washing the filaments while they progress on the rollers until their content of low molecular weight fractions and foreign substances is reduced to the desired low value, and means for completely cold-drawing the washed filaments. As shown in Fig. 1, a thread 10 of melt-spun synthetic linear polymer is taken from bobbin 11, or is taken directly from the extrusion apparatus, and passed to the washing unit 13. The thread is passed in substantially helical turns around a main roller 14 and one or more auxiliary rollers 15. As the thread advances axially along the roller 14 it is showered with washing liquid from a perforated pipe 16. The washed thread passes from the washing unit to a stretching device comprising pairs of nip rollers 19, 20. The stretched thread passes to a drying unit 21 which comprises a pair of thread-storage, thread-advancing rollers 22, 23. Means for circulating a heating fluid within roller 22 may be provided. If desired, the thread may be additionally stretched between the rollers 20 and the drying unit 21. Alternatively, the rollers 19, 20 may be omitted and the stretching may be effected directly between rollers 14, 15 and rollers 22, 23. If desired the main stretching treatment may be effected after the thread has been dried. As shown in Fig. 3, bundles of filaments from a number of bobbins 30 are brought together by means of a guide 32 to form a sliver 33. The sliver is wetted with water as it passes through channel 34. The water may be at a temperature of 45-70 DEG C. The sliver then passes to the washing unit which comprises thread storage and advancing rollers 36, 37 and means for showering the sliver with water. The washed sliver then passes between two sets of cylinders 53, 54, which effect the desired cold-drawing, preferably at a temperature not higher than 70 DEG C. To prevent adhesion of individual filaments, the last cylinder of the set 54 (i.e. cylinder 55) may be provided with an uneven surface, e.g. it may have longitudinal indentations or grooves. The cylinders and also the rollers 36, 37 may be covered with felt or rubber. A mobile guide 56 with transverse alternating motion is provided to avoid uneven wear on the surfaces of the cylinders. The stretched sliver passes to a drying unit comprising a drying roller 57 and a secondary roller 58. Heating fluid may be circulated through the hollow roller 57 or may be directed on to the sliver as it passes over the roller, or heating may be effected by radiation or by dielectric heating devices. Roller 57 may be tapered to allow for shrinkage of the sliver during drying. The dried sliver passes through a crimping device 59 and then to a cutter 60 which converts it to staple fibre. If desired, a single cold-drawing unit such as the assembly of cylinders 53, 54 may operate on a plurality of bundles or slivers of filaments, and for each bundle of filaments there may be provided a separate washing unit. Friction rollers or other devices may be provided in association with the stretching devices for localizing the draw-point. To facilitate recovery of the monomers and low polymers from the wash liquor, the filament, thread or sliver may be subjected to counter-current washing. Thus, fresh water may be showered on the turns of sliver in a zone adjacent the delivery end of the washing roller, and the liquid which drains off the roller in that zone is collected and pumped to a spraying device at an intermediate zone of the roller. The liquid draining from this zone is similarly collected and then sprayed on to the turns of sliver in a zone adjacent the receiving end of the roller. The liquid draining from this zone is collected and treated for recovery of the substances which have been washed out of the sliver.