An apparatus for the heating of plastics material pre-forms comprises a movable carrier on which is arranged at least one heating device, the heating device including a holding element for holding and conveying the plastics material pre-forms. A heating cavity is included, into which individual plastics material pre-forms can be inserted. A moving device is suitable for inserting the plastics material pre-forms into the heating cavity. A clean room, inside which the plastics material pre-forms are capable of being heated by the heating cavity is included, wherein the clean room is isolated from an external environment by at least one first wall and at least one second wall, the second wall being constructed and arranged to be movable with respect to the first wall.