Abstract: Yarns and fibers based on atactic polyvinyl chloride possess a residual shrinkage in boiling water of less than 3%, a modulus of elasticity which is greater than or equal to 2 kN/mm.sup.2, an orientation index of the crystalline zones which is greater than or equal to 70%, an orientation index of the mesomorphic zones which is greater than or equal to 8%, and an orientation index of the amorphous zones which is greater than or equal to 5%. They are obtained by spinning and stretching in a known manner, then stabilization under tension at a temperature between 105.degree. and 130.degree. C., in the presence of steam under pressure, for 1 to 3 seconds, and then shrinkage in an aqueous fluid medium at a temperature between 98.degree. and 130.degree. C.

Abstract: Acrylic yarns and fibers having a high shrinkage power, ranging up to 50%, obtained by wet spinning, a stretching of 1.3 to 3 .times. in air, washing, a stretching of 1 to 2.5 .times. into boiling water, drying, steaming at 105.degree.-150.degree. C., over-stretching of 1.2 to 2 .times. at 90.degree.-100.degree. C.