Abstract: A process and device is provided for cooling extruded hollow sections, especially pipes, that are made of plastic. Liquid or supercritical carbon dioxide is directed into the interior of the plastic hollow section through an extruder head and is depressurized in at least one depressurization nozzle, whereby carbon dioxide in gaseous and solid form is produced. The carbon dioxide that is in gaseous form is directed to the inner wall of the hollow section, while carbon dioxide snow is brought into heat exchange with the inner wall of hollow section only to the extent that the latter is not damaged.