Highly oriented high-density polyethylene (HDPE) and polypropylene (PP) were obtained by solid state extrusion near, but below, the melting temperature. Draw ratios of 6 and 11 were obtained using properly designed dies, preformed billets and lubrication for different extrusion temperatures. Orientation induced significant changes in properties and morphology that are related to the final draw ratio. The draw ratio was observed to decrease with an increase in extrusion speed due to the molecular relaxation occurring because of local heating during deformation. An increase in the degree of crystallinity was observed for the oriented polymers as well as a large improvement in the tensile modulus. Significant molecular relaxation and elastic recoil were observed during processing. Extrusion speed strongly increases the extent of relaxation, and, consequently, reduces many of the mechanical properties.