The water sorption mechanism in thin nylon 6 films is studied by 1H NMR imaging and relaxometry. Experiments using D2O and H2O enable identification of polymer and water signal components during the uptake process. Tracking the mobility and size of polymer and water components gives new insights into the water sorption mechanism of nylon 6. 1H NMR imaging and relaxometry it is shown that water uptake is faster than plasticization. Water arrives first in the polymer matrix. After a while plasticization starts. Plasticization continues even when the nylon matrix is fully saturated. Further it is observed that the water mobility is still increasing, when the matrix is both saturated by water and plasticized.