of the present invention there may be included heat treatments to cause stalibization or relaxation sizing fixing or cooling treatments spraying with particles or the like the apparatus of the instant invention permits heat treatment of long lengths of yarn within a limited space thus as shown in fig9 two cylinders 1 are used for heat treatment of the yarn 6 which passes through two sets of false twist nozzles 8 in this case the orifices 3 in the internal faces of the grooves may be blocked the two cylinders are mounted on a support 7 in operation the yarn is hooked up to a take up or winding device and the fluid pressure in the chamber 4 is increased to suspend and advance the yarn the take up then winds the yarn in a conventional way as the yarn is advanced the present example describes the relaxation heat treatment of a multifilament yarn of 2 300 dtex 136 strands texturized by the process described in u s pat no 3 703 754 in which after texturizing the compression effect is eliminated by subjecting the yarn to relative tension by passing it between two rollers the treated yarn is then wound up on a bobbin the yarn is used for the manufacture of needle punched or tufted carpets in which it is desirable for the loop formed by the pile to have good elasticity good covering power.