The effect of product characteristics and processing conditions on the initial rate of water absorption of 15 clay bricks was investigated and the influence of porosimetric parameters (amount, size and tortuosity of pores) as well as of phase composition (amount of calcium-silicates and amorphous phase) was established. The suction behaviour of bricks, which may be brought back to the models of [Gummerson RJ, Hall C, Hoff WD. The suction rate and the sorptivity of bricks. Brit Ceram Trans J 1981;80:150-2.] and [Hoffmann D, Niesel K. Quantifying capillary rise in columns of porous material. Am Ceram Soc Bull 1988;67(8):1418.], was also evaluated on the basis of both the product microstructure and the liquid physical properties. According to the model of Beltran et al. (1988), which reveled to be sufficiently reliable, the values of the capillary coefficient K s were calculated and their correlation with the experimental ones has been provided. For a given liquid and in the same experimental conditions, the results indicate that varying in a controlled way the product microstructure (i.e. decreasing the pore size, increasing the pore tortuosity and/or controlling the amorphous/new formed phases ratio) should allow to design materials having a most suitable behaviour.