Abstract: The invention relates to a method in connection with a process for insulating or sheathing conductors or the like, wherein plastic material is extruded into at least one layer on the surface of the conductor (1), and the conductor coated with the plastic material (2, 3, 4) is cooled in a predetermined manner. To avoid problems caused by the shrinking of the plastic material, after the cooling of the conductor (1) and the plastic material in vicinity to it to a predetermined level in the insulating or sheathing process, the surface layer of the plastic material and the plastic material portions in vicinity to it are reheated to a predetermined temperature in a pressurized space filled with a medium.