Abstract <p>The influence of the pore size of a nanoporous material and the rate of change in the internal volume of the nanoporous material–nonwetting liquid system on the filling pressure of the nonwetting liquid (distilled water) of hydrophobized nanoporous materials with pore sizes of 9 nm (Fluka 100 C8), 5 nm (Fluka 60 C8 PF), and 2 nm (MCM-41-C1) at rates of change in the volume of the nanoporous material–nonwetting liquid system of 2.7 × 10^–4, 2.7 ×10^–3, and 2.7×10^–2 cm³/s was studied. It was shown that decreasing the pore size increases the characteristic pore filling pressures, which follows from the classical theory of capillarity. It was also found that increasing the rate of change in the internal volume of the nanoporous material–nonwetting liquid system leads to an increase in filling pressures for all systems with an increase in the rate from 2.7 × 10^–4 up to 2.7 × 10^–3 cm³/s, but further increase in rate to 2.7 × 10^–2 cm³/s leads to an increase in filling pressures only for MCM-41-C1, while for other systems this increase is within the measurement error. Based on the results obtained, it can be concluded that there is a transition from a quasi-static to a quasi-dynamic filling mode. It is also possible to assume the existence of a critical pore size that determines condition for the growth of filling pressure with an increase in the rate of change in the internal volume of the system.</p>