The warping effect of high-density polyethylene (HDPE) articles produc
ed by organic pigmentation has been studied by scanning electron micro
scopy. A warping pigment and its warp-free analogue obtained by surfac
e treatment have been observed and compared to an inorganic warp-free
pigment. The results indicate that the generally accepted nucleation t
heory is not sufficient to describe fully the warping effect. An attem
pt is made to describe this effect in terms of pigment-polymer compati
bility.