AbstractThe Melting of various polyethylene structures is compared by using data obtained on the Perkin‐Elmer differential scanning calorimeter (DSC). Transparent, high‐density samples crystallized under both orientation and pressure in the Instron capillary rheometer are compared with samples crystallized from dilute solution by stirring and with samples crystallized under high pressure. The latter two structures are assumed to contain extended‐chain crystallites. By comparison, the melting points and the superheatability of the Instron samples are consistent with the presence of an extended‐chain crystal component. The melting of irradiated samples crystallized in the rheometer is also observed to be consistent with this conclusion. In addition, DSC data are compared with the melting points defined with a polarized light microscope equipped with a hot stage.