a method is proposed for sterilizing packaging material of plastic , cardboard or combinations of the two , in particular for sterilizing preshaped packaging containers intended for receiving acidic products . in this method , damage to the packaging material or the packaging apparatus is to be avoided because of the mild thermal treatment involved . by subjecting the surface to be treated to a flow of a moist mixture of water vapor and air at a temperature of from 80 ° to 140 ° c . and having a moisture content of from 5 to 50 %, sufficiently high degrees of sterility for the sterile packaging of acidic food products are attainable within relatively short treatment periods .