Spiral fed multi-layer tubular die

Extrusion die apparatus for extruding a multiple layer tubular product comprising an elongated cylindrical mandrel (12) and annular die elements (A-D) mounted coaxially one behind the other on the mandrel forming thickness control passages (47-50) between the die elements and the mandrel. The die elements have rearwardly inclined inner (38) and outer (34) conical surfaces and are nested together with the outer conical surfaces of one die element facing the inner conical surfaces of an adjacent die element. The conical surfaces form conical passages (53-55) therebetween which communicate with the thickness control passages. A helical groove (36) is provided on the outer conical surface of each die element. Means are provided for delivering a molten thermoplastic material to the conical passages. The molten material is preferably delivered from an inlet (94) to a plurality of outlets (P1-P8) on each die element by a binary divider system dividing (88) the flow of molten material into separate paths.