Tensile fracture and punch shear failure surfaces have been observed in a scanning electron microscope. In most cases tensile cracks were visible in the shear fracture surfaces and crack initiation points could be found in the tensile fracture surfaces. The punch test imposes very large shear strains on the materials (many thousand percent) and this appears to reorient the chains so that, so long as the chain length is great enough (>4000 repeat units for polyethylene), chain scission is observed, and the failure process at the molecular level is tensile rather than shear. The exceptions are the shorter chain polyethylenes and polypropylene, which are probably truly liquid-like, with little or no chain scission being involved in tension or shear.