AbstractThe course of melting of melt‐crystallized polyethylene fractions and of a poly(ethylene oxide)‐polystyrene‐poly(ethylene oxide) triblock copolymer has been followed by small‐angle x‐ray scattering (SAXS). Changes in the intensity and shape of the SAXS curves indicated that both surface melting and melting over the full crystallite thickness (full‐strand melting) take place. Full strand melting is the final, irreversible process. Comparison with an analytical model indicates that in the earlier stages of the irreversible, full‐strand process the crystallites melt out randomly throughout the bulk. Later stages may occur by the simultaneous melting of a larger stack of