A device and a method for producing a preform having a shoulder and base geometry optimized for subsequent stretch blow molding, since the preform cannot be produced according to the conventional injection-molding method. For this purpose, the preform produced in the injection-molding tool is transferred into a conditioning station and is conditioned and cooled in the shaft while no contact is made with the top of the preform and the preform shoulder on account of a special contour of the conditioning receptacle. Due to the reheating of these preform regions they can be mechanically deformed into a new geometry which is advantageous for the blow molding process and thus their wall thickness can also be influenced. In the subsequent blow molding process the deformed preform has the advantage that the plastic material which is distributed better in the bottle results in considerable material savings and higher quality bottles.