A packing or seal stack for a pump includes alternating first type and second type packing rings of polymer material such as ultrahigh molecular weight polyethylene (UHMWPE). The first and second type packing rings have essentially identical geometry, and the second type packing rings are lubricant filled polymer material. The geometry of the packing rings creates, when the packing rings are stacked, contact points that are positioned in a core area near a body center line of the ring bodies. Gaps are formed so that the packing rings do not contact one another near the inner and outer radial portions of the packing rings.