Abstract: Extruded web multiple panels are produced with undulated webs by extrusion of a thermoplastic material by a device including an extruder, a slotted die connected thereto which comprises core pieces in the die slot for forming the webs, a movable mold channel placed downstream of the slotted die, and a removal device. The undulation of the webs is produced by friction forces rhythmically alternating in direction crosswise to the extrusion direction. The friction forces are allowed to act in the mold channel on the extrudate in an area where it is still above its softening temperature. The friction forces are produced either by a rhythmic crosswise movement of the entire mold channel or by movable sections of the mold channel walls of a special mold channel.