Abstract: The apparatus and process to compensate for variations in thickness of molding tools and of moldable materials used in an embossing process to be carried out under a vacuum, while ensuring high dimensional stability, and to ensure different molding depths. For achieving this object, a chamber is employed having a pair of oppositely lying chamber parts, of which one is fixed to the framework and the other is adjustable, having side walls which comprise an inner part and an outer part. The inner part is fastened to the fixed chamber part and the outer part, on the outwardly facing end face to of which the adjustable chamber part comes to bear against the force of a spring during the closing of the chamber, is displaceable along guide elements on the fixed chamber part between two stops.