Abstract: This invention discloses an extruder head having a cavity whose shape can be visualized with reference to a model. The model is a circular tube having a wall thickness which is constant at any given distance from one end. The tube is split longitudinally at or near one end and unfolded gradually into the form of a flat sheet at the other end. Extrudate which enters the cavity in a solid, circular cross-sectional configuration is shaped into the form of the unsplit portion of the model by a mandrel in an entrance zone. A divider splits the extrudate longitudinally. The cavity continues as a transition zone in which the split tube of extrudate is unfolded gradually to become a flat sheet in an exit zone. Variations in the shape of the cavity in the exit zone are presented in which the extrudate is formed into shapes more complex than the flat sheet.