pass through the treatment zone the filaments of the primary yarn are therefore separated from each other and the filaments of the secondary yarns are blown about and whipped violently in such manner that the individual filaments are first separated and then swirled into crunodal ring like loops and other convolutions which interlock the filaments of the secondary yarn and also interlock these filaments with the filaments of the primary yarn which are separated by the turbulence but not themselves formed with convolutions the bulky yarn is then wound into a package on a take up mandrel 34 at the rate of 500 meters per second with a method such as this the input titre of the constituent yarns is 334 decitex and the final titre of the bulky yarn is 378 decitex although not shown it is also possible to subject the composite bulky yarn issuing from the air nozzle device 24 to heat treatment as described with reference to the apparatus illustrated in fig1 and 2 the bulky yarn 31 produced by this method has an appearance which is similar to that schematically illustrated in fig3 as shown in fig4 filaments 1a and 1b representing two of the 68 filaments of the primary yarn 1 are separated from each other so as to permit the insertion of convolutions formed in the filaments of the secondary yarn 2 but are not themselves formed with crunodal ring like loops the filaments 2a shown in fig5 represent two of the 68 filaments of the secondary yarn 2 and show the formation of randomly spaced crunodal ring like loops 2c along the lengths of the filaments after formation of the loops.