This work deals with the role of liquid water on the microstructure of a semiaromatic polyamide (MXD6). One side of injected plates is kept in contact with water during different durations. After immersion, microtomic cuts are performed at different depth and are analyzed by X-ray diffraction, differential scanning calorimetry, and permeation tests. Measurements show that the water plasticizes the initially amorphous plates and induces a spherulitic crystallization, which grows from the wet side to the dry one. As a consequence, the permeation curve is unusual, and the water flux goes through a maximum before reaching a lower plateau when the front of crystallization reaches the opposite dry face. (c) 2005 Wiley Periodicals, Inc.