This study presents the kinetic sorption behavior of six different gases (CO2, C3H8, C3H6, Xe, Kr, and Ar) in films of the glassy polyimide Matrimid using a magnetic suspension balance. The dynamic mass uptake was analyzed using a model discriminating and quantifying separate contributions of Fickian diffusion and relaxations. The model provides a quantitative insight into the pressure/concentration-dependent onsets and relative magnitudes of sorption-induced relaxations. We demonstrate that any gaseven noble gasesshow non-Fickian diffusion and may induce irreversible sorption relaxations upon reaching a critical amount of volume dilation. Above this critical amount of volume dilation, kinetic sorption behavior becomes non-Fickian. For all gases studied, this critical volume dilation is unique.