A biodegradable polyester, poly(tetramethylene dodecanedioate), was injection molded in a rectangular cavity. Thin sections were sliced from molded samples starting from the skin. The morphology distribution inside the molded samples was studied by X-ray analysis. The diffusion and solubility coefficient of water vapor were then measured using the microgravimetric method at the temperature of 30 degrees C. Results show that morphology developed during the process influences the diffusion of water molecules through the polymer matrix. In particular, a direct influence of crystalline degree on the sorption and diffusion parameters was identified. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 117: 2831-2838, 2010