a plurality of extrusion dies are operated from the same source of heat - plastified polymeric material , e . g ., from a single barrel extruder , via a distribution manifold which includes forwardly diverging flow passages each leading to a different one of the dies . the flow passages of the manifold have equal flow capacities and compensation for differences between the extrusion dies is accomplished by equipping each die assembly with a replaceable flow control insert , the inserts being so dimensioned that the pressure differential across each die assembly , including the insert , is the same .