A detailed inspection of the microstructure of polyamide and polyimide aerogels related to applications in humid environment was carried out and centered on their hydration mechanism. The structures of these porous materials remain intact under hydrated conditions. The two synthetic aerogels were characterized in the dry state by IR spectroscopy, Nitrogen adsorption-desorption porosimetry and scanning electron microscopy (SEM). As an indirect approach to study the hydration induced structural changes, the aerogels were hydrated stepwise, and investigated by liquid-state nuclear magnetic resonance (NMR) relaxometry. From the relaxometry measurements, we can get information on the different structural regions in association with bound water, and therefore, on the hydration mechanism of the aerogels.