thickness of a needled sheet 20 such as for example 8 times and typically less than the total number of sheets to be stacked the needling depth is kept constant throughout the entire operation due to the progressive lowering of the structure with respect to the needles it is necessary for needling the first sheets on the platen 10 to provide means preventing the needles 13 from abutting against the hard surface of the platen 10 to this end the platen 10 is provided with a top layer 11 into which the needles can penetrate without any risk of being damaged and without carrying back particles or fibers into the structure to be produced said layer 11 can for example comprise a sheet 11a of reinforced elastomer such as for example reinforced 34 hypalon 34 or a 34 nylon 34 material fixed to the platen 10 and on which is adhesively fixed a layer 11b formed of a felt base for example a polypropylene felt o sufficient thickness for the needles to penetrate during the first needling strokes through the provided needling depth without touching the platen 10 on said felt base is adhesively fixed another sheet 11c for example of polyvinylchloride during the needling the sheet 11c is traversed through by the needles but inhibits fibers from the material of the sheets 20 being thrust into a linking with the felt base which would complicate the separation of the completed structure from the layer 11 it will be noted as a variant that.