The macroscopic physical modeling of humidity-, energy-, and air-coupled transport in unsaturated porous materials requires their water retention characteristics and transport coefficients to be known. Among the most sensitive properties are the air and liquid permeabilities.As their direct determination is often difficult and time consuming, relations have long been proposed starting from experimental properties that are easier to obtain, such as water pressure head as a function of the degree of saturation or isothermal sorption curves.In the first part, existing model relationships are compared with experimentation. The data obtained show that a parameter in these relationships has to be modified. The proposed modifications are interesting for practical applications, but the authors have also tried, in the second part of the study, to generalize the approach by starting from the porosity of the cement-based materials studied here.Expressions for the relative permeabilities are given as functions of tortuosity and capillary pressure, which can be deduced from the pore size distribution.An expression is proposed for the tortuosity. The relative influence of the porosity and the tortuosity of the cement-based materials on gas and liquid permeabilities, according to the relative degree of saturation, are discussed.