AbstractThe effects of thermal treatment in the 70–90°C. region on polybutene‐1 crystals, prepared by precipitation from dilute pentyl acetate solutions and with lath, hexagonal, and square morphologies, have been studied by using electron microscopy. The stability of polybutene‐1 crystals to thermal treatment increases in the order: lath < hexagonal < square. Elucidation of the crystallographic directions in unheated lath crystals with respect to the overall morphology was carried out; evidence for restricted folding in these crystals is discussed.