Abstract: To cover at least one face of an extruded, hollow, plastic body, the front face of the extruder die is formed with a recess in which a cylindrical roller is rotatably mounted contiguously adjacent the die orifice. The roller defines a first portion of a feed channel for a foil with the die wall in the recess and a second channel portion, tangential to the first, with the mandrel which defines an extrusion gap in the die orifice. The foil may be draped about side faces of the mandrel by pressure rollers if the extrudate is backed by mandrel portions extending to the pressure rollers.