the invention relates to a method and a device for manufacturing multi - ply sheets of extrudable plastics material supplied by way of at least two webs which are produced by extruders having flat sheet dies and which are bonded to a structured insert web by means of rolls . moreover , the invention relates to multi - ply sheets thus produced , especially for use with a shower enclosure . in manufacturing such multi - ply sheets it is difficult to obtain a reliable bond between the webs and the structured web without sophisticated machinery . there is also the requirement that the structured web be uniformly introduced between the webs . the invention proposes to feed these webs to a single common set of rolls and to arrange the flat sheet die of at least one extruder so close to a set of rolls that a reliable permanent bond to the structured web and / or at the other web is obtained by the heat accumulated and carried in the one web just extruded .