Abstract: As exemplified by an automobile engine oil filter, the usual pleated filter paper is internally supported by an interpleated layer of high tear and tensile strength material which is substantially more flexible than the paper. With the ends of both layers anchored conventionally in the element's end caps rigidly held apart by the usual perforated center tube, the flexible material is subjected to a tensile stress when the paper attempts to move inwardly, the paper being thereby supported against rupturing or pleat tear. The flexible material thus functioning as a back-up layer for the paper, can be pretensioned to provide greater additional resistance to inward movement of the paper.