Two polyethylene and two polypropylene melts were characterized in uniaxial elongational flow. They exhibit significant differences with respect to strain hardening. For the polypropylenes it was shown that the elongational behavior found in uniaxial elongation is qualitatively reflected in biaxial deformation too. From the polyethylenes, films were blown using laboratory equipment, and the polypropylenes were processed into beakers by thermoforming. For both materials it could be shown that strain hardening is of advantage for the geometrical uniformity of the processed items.