In this study, attention is directed towards the abilities of elongational flow to induce the chain orientation and, as a consequence, to improve the properties of extruded profiles. A novel-designed extrusion die with semihyperbolic convergency of the channel, by which a high percentage of elongational flow in the melt is generated, was connected with a conventional single-screw extruder. Commercial grades of high-density polyethylene and isotactic polypropylene were used as model commodity polymers. Round extrudates prepared by this processing line were assessed as self-reinforced products. Detailed structural observation carried out with the aid of scanning electron microscopy and wide-angle X-ray scattering evidenced that the structure of extruded rods is uniquely fibrous and highly oriented throughout the profile. As a result, the self-reinforced extrudates possess outstanding storage modulus in a wide range of temperatures and considerably higher melting point and fusion heat than rods produced by conventional extrusion.