Superabsorbent polymers (SAPs) are a promising additive to be used in the building industry but may induce microstructural changes. Water vapour sorption may be used to characterize the change in pore structure of cementitious materials, but the technique is difficult to interpret. In the present paper, static and dynamic vapour sorption (DVS) measurements were performed and compared to nitrogen adsorption experiments. The models of Dubinin-Radushkevich and Barrett-Joyner-Halenda were hereby applied to study pores in the micro- and mesopore range. The results show that cement pastes with SAPs and without additional water show a slight decrease in porosity in the micro- and mesopore range. Cement pastes with SAPs and with additional water show no significant change of porosity in the micropore range and a slight increase in the larger mesopore range. These new findings give insight into the effects of SAPs on the microstructure and strength of cementitious materials.