in the schematic diagram of fig1 two extruders 2 , 4 are shown which include flat sheet dies 6 , 8 . there latter are parallel to each other and extend over a given width of , say , 2 m in a direction vertical to the drawing plane . through these dies 6 , 8 , the extruders 2 , 4 supply in a conventional manner webs 12 , 14 of plastics . an unwinder 16 is provided for supplying a further structured web 18 . in particular , the structured web is of textile material such as curtain cloth . alternatively , the structured web may be a plastic foil carrying a texture , a printed pattern or a color pattern , as the case may be . it is possible to prefabricate such structured webs and to insert them , by way of reels , into the unwinder 16 . the structured web 18 is taken off by means of a feeder 20 . downstream of the two extruders 2 , 4 there is a common laminator 22 . as a rule , it contains three rolls 24 , 26 , 28 for smoothing and , i . e . being chill rolls , chilling also for a plastics web introduced . in accordance with the invention , the webs 12 , 14 supplied from the flat sheet dies 6 , 8 are fed together with the structured web 18 to the laminator 22 , with the structured web 18 being sandwiched between the two outer webs 12 and 14 . in this way , perfect bonding of the two webs 12 , 14 including the structured web 18 is achieved . a roller conveyor 30 is arranged downstream of the laminator 22 for finally cooling down a multi - ply sheet 32 thus manufactured . in addition , take - off rolls 34 are provided for some stretching of the sheet 32 in order to prevent its slacking or corrogating . the take - off rolls 34 are followed by further units and plants such as trimming tools , stacks , etc . which are not shown as they do not directly contribute to the invention . attention is drawn to the fact that a multi - ply sheet or panel 32 comprises three plies corresponding to web 12 , structured web 18 and web 14 . preferably , at least one of the webs is of a transparent or light transmitting plastics material so that the inner structured web will be visible from outside . for instance , if the structured web is a curtain cloth having a woven or knitted pattern , the latter will be directly perceptible . as the thickness of the webs 12 , 14 corresponds to the setting of the flat sheet dies 6 , 8 , the structured web 18 will always be in a predetermined region within the multi - ply sheet 32 produced . since the webs 12 and 14 with the structured web 18 sandwiched therebetween are fed into the laminator 22 , any irregularity of the assembled panel or multi - ply sheet 32 is prevented . the diagram of fig2 shows an embodiment including a coater 36 by means of which a pattern is first applied to the inside surface 38 of web 14 . preferably , the coater 36 is a printing unit for applying a color coat or color coatings onto the inside surface 38 of web 14 in a conventional manner . this involves the use of a print roll 40 schematically indicated , whereas color or ink feeders , distributors , etc . are not shown in the drawings . expediently , the coater 36 is arranged at a distance to extruder 4 so that the inside surface 38 will be moderately chilled when the color coats or patterns are applied . the embodiment according to fig3 features a distributor 42 for spreading particles onto web 12 into which they may be rolled by means of a laminator 23 . the particles may be preformed , e . g . small plastics balls , rods or other shaped parts , which may also incorporate dye substances . if these particles are spread and fed together with the plastics webs 12 , 14 to the laminator 23 , corresponding patterns are formed . alternatively or additionally , the distributor 42 may be used to spread or spray dye particles onto web 12 for generating or modifying a pattern . further , as indicated in fig3 the central roll 27 of laminator 23 may have an embossed periphery or profile 44 . such a profile permits applying a pattern to the outer face of the final multi - ply sheet 32 as well . combined with an inner structured web 18 introduced by the method according to the invention , such an outer pattern will create special optical effects . another embodiment is shown in fig4 wherein on a roller conveyor , coating means 46 are provided for applying color patterns onto the outer face of web 12 . the coating means 46 may be a print roll to which a color or ink may be supplied in a conventional way ( not presented ). further , uncoating means 48 are arranged downstream of the coating means 46 for at least partially removing again the color patterns applied previously . the uncoating or abrasion means are adapted to reciprocate , particularly in the direction of double arrow 50 , at the lower or bottom side of web 12 . this reciprocating motion is performed at a relatively high speed and under a certain contact pressure . color or dye particles thus abraded may be collected by means of a belt 52 in the interior of uncoating means 48 . at timed intervals , the belt 52 is moved on so that fresh portions of the belt 52 will be available for collection . it is emphasized that the application of color patterns onto the outer face of a panel as described may also be performed with a single - ply material . if the color patterns are applied to a structured or texture outer face , this will lead to particularly favorable results since the color pattern is substantially retained in the sunk regions of the outer face , whereas the color or dye particles are largely removed from the raised portions of the outer face by the abrasion or uncoating means . from the schematic diagram of fig5 a preferred embodiment will be seen in which laminators 23 and 22 , respectively , are arranged downstream of the extruders 2 and 4 , respectively . laminator 23 comprises a central roll 27 with a peripheral profile 44 . it will be evident that web 12 issuing from laminator 23 has a structured surface 58 . by contrast , laminator 22 includes three smooth rolls ( 26 ) so that web 14 issuing therefrom also has smooth surfaces . now the two webs 12 and 14 are jointly fed to a set of rolls 60 , 62 . upstream of these , however , there is an applicator 56 by means of which an adhesive 54 may be spread or sprayed onto the structured surface 58 of web 12 . the clearance between the rolls 60 and 62 is selected such that the adhesive 54 introduced therebetween will have a predetermined optimum thickness . at the same time , rolls 60 , 62 serve to provide the pressing force for achieving a reliable bonding of webs 12 and 14 . the distance of the set of rolls 60 , 62 to the laminators 22 , 23 is dimensioned to warrant that at least the surfaces of webs 12 , 14 are moderately chilled in order to exclude a substantial change or modifications of the structured surface 58 of web 12 . it will be seen that the webs after passing through the set of rolls 60 , 62 are joined to each other to form a multi - ply sheet with substantially smooth outer faces . the structured surface 58 is within the final multi - ply sheet which , in spite of its smooth outer faces , has the same appearance as a conventional sheet with a structured outer face . preferably , the adhesive 54 includes suitable dye substances to obtain color effects , if such are desired . further , it will be evident that the means and measures elucidated above with reference to fig4 may be suitably combined with the device according to fig5 . similar to the manner elucidated above , coating means ( 46 ) and uncoating means ( 48 ) may be arranged between a laminator ( 23 ) and a set of rolls ( 60 , 62 ). thus color patterns will be applied to the structured surface ( 58 ) of web 12 , and only in the raised portions of the structured surface ( 58 ) will the uncoating means ( 48 ) be operative . a multi - ply sheet thus manufactured is distinguished by special optical effects and a peculiar appearance . the method and the device for manufacturing it do not , however , require particular expenditures . reference is made to the fact that within the scope of the invention , the webs may be supplied from the extruders via means other than elucidated above . thus it is possible to arrange downstream of the extruders -- i . e . without any flat sheet dies -- calenders or other sets of rolls which may even replace the laminators . however , all the embodiments of the invention are characterized by sandwiching a structured web , a pattern or the like in between the webs supplied and the assembled webs are subsequently joined or bonded to each other by suitable roll means . the perspective view of fig6 shows the example of a shower enclosure having a profile frame 102 with an upper profile rail 104 in which three door sections 106 , 108 , 110 may be shifted . these sliding door sections 106 , 108 , 110 are shown here in a pivoted position , the vertical pivot axes being designated by 112 , 114 , 116 . normally , the door sections 106 , 108 , 110 are at a right angle to the position shown so that the upper front edges 118 , 120 , 122 are essentially parallel to the upper profile rail 104 . by suitable guiding means ( not shown ), the door sections 106 , 108 , 110 may be slid along upper profile rail 104 for providing an entrance to the shower enclosure . the profile frame 102 may rest with its lower profile rail on top of the brim of a shower or bathtub , and lateral profile rails 126 , 128 serve to secure the profile frame 102 by suitable means ( not shown ) to the walls of a building . it is possible to attach one of the lateral profile rails 126 , 128 or both with a wall component ( not shown ) arranged at a right angle to the lateral profile rails 126 , 128 . the door sections 106 , 108 , 110 comprise inset frames 130 , 132 , 134 containing panels 136 , 138 , 140 . as will be explained below , these panels 136 , 138 , 140 consist of a plurality of plies with an inner or insert ply 146 being visible through transparent outer plies 142 , 144 . fig7 shows a vertical sectional view along the line ii -- ii of fig6 representing door section 106 . it will be realized that panel 136 comprises two outer plies 142 , 144 of a light transmitting or transparent plastics material . an insert ply 146 is sandwiched between the outer plies 142 , 144 . in the embodiment shown , this insert ply 146 is a textile material , viz . a curtain cloth indicated in fig7 to be a fabric of trellis or filament structure . for the sake of clarity the cloth is indicated at a larger scale , the woof threads being designated by 148 and the warp threads by 150 . the outer plies 142 , 144 and the insert ply 146 are solidly bonded to each other due to the warm treatment , the use of rolls or the like in the manufacture of panel 136 . in this process , the insert ply 146 , i . e . the curtain cloth , is at least partially penetrated by the outer ply plastics that is relatively soft and shapable at this stage . since the outer plies 142 , 144 are of a light transmitting or transparent plastics material , the pattern of the insert ply 146 , viz . the curtain cloth design , is fully visible from outside . on the other hand , this curtain cloth is protected by the plastics plies 142 , 144 against ambient influences , in particular against penetration of moisture or accumulation of dirt . moreover , it is important to note that the outer faces 152 , 154 of panel 136 are substantially smooth . therefore , inset frame 130 may be directly and tightly joined to the outer faces 152 , 154 . for additional safety against the penetration of dirt and / or moisture between inset frame 130 and panel 136 , it is possible to insert suitable seals that will definitely exclude any contamination or the penetration of germs . as an alternative to the curtain cloth schematically indicated in fig7 the insert ply 146 may also consist of different materials . thus the insert ply 146 may comprise a plastic foil suitably provided with a color pattern . also , insert ply 146 may be a color coat applied to one of the outer plies 142 , 144 . a plurality of outer plies and of insert plies may also be provided within the scope of the invention . for example , where a first insert ply of a textile material or cloth is used , a color coat or several color coats may be applied to the inside ( s ) of the outer plies 142 , 144 . yet other alternatives include insert plies 146 comprising a wire cloth that will most favorably increase the stability of the panel and thus of the entire shower enclosure . expediently , the material of such a wire cloth may be aluminium or copper which lend themselves to relatively easy working and will permit cutting or sawing the panels to the dimensions required without the use of special tools . furthermore , the insert ply 146 may be a metal foil provided with desired patterns that may , in particular , be embossed . by means of the outer plies , such a metal foil , too , will be excellently protected against corrosion , deterioration or soiling . the schematic elevation of fig8 shows a particularly important embodiment of the device according to the invention , with the set of rolls being a laminator 22 having three rolls 24 , 26 , 28 . the flat sheet dies 6 , 8 of the extruders ( not shown ) are partly indicated . it will be seen that the associated extruders are arranged at one side each 72 and 74 , respectively , of laminator 22 . the flat sheet dies 6 , 8 are in the immediate proximity of the roll nips 64 and 68 , respectively , so that the two webs 12 , 14 may be directly fed into these roll nips of the laminator . to the first roll nip 64 , a structured web 18 is fed together with web 12 . it is to be emphasized that structured web 18 as supplied from unwinder 16 contacts the lower roll 24 over a predetermined peripheral angular range 66 prior to entering the roll nip 64 . this serves to reliably orient the structured web 18 as it enters the roll nip 64 so that plaits , wrinkles , etc . will be prevented and cannot occur in the final multi - ply sheet . further , it will be seen that chill roll 26 , i . e . being unheated , is contacted or wrapped by web 12 as well as structured web 18 over an arc of 180 degrees , this bringing about some chilling of web 12 so that the structure web 18 is preset thereon . next , the other web 14 -- which is still relatively warm at this stage -- is introduced into the roll nip 68 . however , owing to the presetting of structured web 18 on web 12 in accordance with the invention , undue penetration or deformation of web 14 is reliably prevented . a further advantage of the device according to this embodiment is its reduced overall height . the extruders mentioned need not be stacked vertically on top of each other . rather , they are arranged at either side 72 and 74 , respectively , of the laminator rolls 24 , 26 , 28 , as is evident in fig8 from the position of flat sheet dies 6 and 8 , respectively . these latter are , moreover , directly accessible for operation , adjustment and maintenance , viz . die 6 from above and die 8 from below , so that the operator &# 39 ; s work is greatly facilitated . while preferred embodiments have been illustrated and elucidated hereinabove , it should be understood that numerous variations and modifications will be apparent to one skilled in the art without departing from the principles of the invention which , therefore , is not to be construed as being limited to the specific forms described .