The humidity-induced swelling and exchange behavior of a block copolymer thin film, which consists of a zwitterionic poly(sulfobetaine) [poly(N,N-dimethyl-N-(3-(methacrylamido)propyl)ammoniopropanesulfonate) (PSPP)] block and a nonionic poly(N-isopropylacrylamide) (PNIPAM) block, are investigated by time-of-flight neutron reflectometry (TOF-NR). We monitor in situ the swelling in the H 2 O atmosphere, followed by an exchange with D 2 O. In the reverse experiment, swelling in the D 2 O atmosphere and the subsequent exchange with H 2 O are studied. Both, static and kinetic TOF-NR measurements indicate significant differences in the interactions between the PSPP 80 -b-PNIPAM 130 thin film and H 2 O or D 2 O, which we attribute to the different H-and D-bonds between water and the polymer. Changes in the chain conformation and hydrogen bonding are probed with Fourier transform infrared spectroscopy during the kinetics of the swelling and exchange processes, which reveals the key roles of the ionic SO 3⁻ group in the PSPP block and of the polar amide groups of both blocks during water uptake and exchange.