At least one blow-molding station is arranged on a conveying device. The blow-molding station includes a blow-mold that forms a cavity into which plastics material pre-forms are expanded by a gaseous medium, supplied by a stressing device. A clean room at least partially surrounds the blow-molding station. A stretching unit stretches the plastics material pre-forms along their longitudinal direction with a stretch bar that is insertable into the plastics material pre-forms. The stretching unit includes a drive device for moving the stretch bar. The blow molding station includes a receiving space with at least one wall for receiving the stretch bar. In operation, the drive device is positioned outside the receiving space at least part of the time. A gaseous medium at a pressure higher than ambient pressure in a non-sterile environment of the receiving space is supplied to the receiving space.