method and apparatus are disclosed for making a laminated board of thermoplastic resin . the laminated board is formed of a pocketed core sheet having inverted and non - inverted pockets disposed between a pair of face sheets which are bonded to the extremities of the pockets . the core sheet is advanced directly from the extrusion die to a roll - forming means which deforms the core sheet to form the pockets in a continuous manner . the face sheets are advanced from the respective extrusion dies on opposite sides of the core sheet and are joined therewith at controlled temperatures so as to form a bond by fusion with the extremities of the pockets . the roll - forming means comprises a drum with multiple convex and concave forming elements with means for vacuum drawing the core sheet against the forming elements and means for forced air removal of the core sheet from the roll - forming means .