A technique for extruding a strip of rubber having filaments embedded therein. The rubber is channeled to an extrusion orifice for forming the strip. The outline of the extrusion orifice presents first and second orthogonal planes of symmetry that intersect at a straight line that is substantially parallel to a direction in which the strip is extruded through the extrusion orifice. The channeling of the rubber can be done with an upstream main channel having the first plane as a plane of symmetry, and extended by two downstream secondary channels that are substantially symmetrical to each other about the first plane. The main channel and the two downstream secondary channels also have the second plane as a plane of symmetry.