A workpiece includes a material with a face and a first plurality of barbs and a second plurality of barbs extending integrally from the face. Each barb has a height above the face. The barbs of the first plurality are at least 10% higher than the barbs of the second plurality. The first plurality of barbs includes at least 10% of the barbs on the face and the second plurality of the barbs includes at least 10% of the barbs on the face. The barbs of the second plurality of barbs are bent and pointed.