Abstract: A process is described for producing filter elements which contain a cross-wound yarn as the filter material, wherein twisted yarn of fine individual fibers is roughened to enhance its filtering action. The yarn may be heat-resistant and the filter element may be used as a soot filter in the exhaust gas stream of an internal combustion engine. Before the yarn is wound up, fiber tufts are broken up by pulling the yarn under tension over a moving roughening surface, the direction of movement of the roughening surface differing by an angle alpha from the direction of movement of the yarn in the area of contact between the yarn and the roughening surface, and the angle alpha being selected in relation to the twist of the yarn, particularly so that the threads of the yarn in contact with the roughening surface are oriented transversely to the direction of movement of the roughening surface. The process produces a roughened yarn which provides the required high filter performance for a soot filter.