from steam generator 7 the fibers softening by the supply of moisture phase b by the action of a drawing force which extends the covering material and is generated by the compression of the seat cushion and the application which is associated therewith of tensile stresses into the covering material an automatic smoothing process takes place after the treatment time provided for the treatment of vehicle seats 1 concerned finishes pallet 2 is conveyed further into a further treatment chamber 11 phase c in which the covering material and vehicle seats 1 are dried in their entirety for this purpose hot air is blown into treatment chamber 11 by means of a fan 12 and a heating system 13 said hot air escaping again on the opposite side of treatment chamber 11 via an outlet connection 14 arranged in outlet connection 14 is a moisture sensor 15 which measures the moisture content of the escaping air and passes it on to a computer 16 the drying process is ended only when the measured moisture has reached a predetermined value pallet 2 is subsequently moved out of treatment chamber 11 phase d vehicle seats 1 can now be conveyed further for installation into the associated motor vehicle according.