Auxetic ultra high molecular weight polyethylene (UHMWPE) is produced via a novel thermal processing route consisting of three stages : compaction, sintering and extrusion. The latter stage, extrusion, is investigated in this paper, with particular reference to the effects of die geometry (cone semi-angle, exit diameter and capillary length) and extrusion rate on the ability of the polymer to produce an extrudate with a negative Poisson’s ratio. It was found that a delicate balance must be achieved between the production of an extrudate which lacks structural integrity and one which is solid but possesses a conventional positive Poisson’s ratio i.e. does not exhibit the nodule-fibril microstructure necessary for auxetic behaviour. In conjunction with the results from the first two papers in this series, it is possible to define a set of conditions required to produce auxetic UHMWPE.