Local orientation measures by infrared dichroism and thermal stress measures by dilatometric analysis of image (DAI) have made it possible to quantify the evolution of the structure versus the thickness of the injected plastic parts. The stiffness local properties on the one hand, and thermal expansion on the other hand, have then been established. Deformation measures made in temperature have pointed out its deformation induced by thermal stresses and that attributed to the gradient of molecular orientation and cristallinity of the polymer. A calculation of plastic part deformation constituted of elementary layers whose Young＇s modulus and coefficients of thermal expansion values have been previously evaluated, has enabled us to corroborate experimental results.