A previous paper (Gómez et al., 2007) details the results of the characterization of two types of lightened clay made by two manufacturers who use different additives. This article shows the results of the characterization of the moisture transfer properties of those same materials. Lightened clay is widely used in the construction sector because of the special characteristics conferred by its porous structure. However, its hygro-thermal properties may very considerably depending on the additives used in its manufacture. The properties measured here are water vapor permeability and liquid water permeability, in accordance with the permeability model (Carmeliet and Roels, 2001), rather than the diffusivity model (De Vries, 1987), using capillary pressure p_c as a driving force instead of moisture content w. On the basis of these two permeability levels, the total permeability of each lightened clay is determined. Water vapor permeability is determined using the `cup' method (UNE-EN ISO 12572, 2002), while liquid water permeability is determined using the inverse method based on Boltzmann's transform, taking the transient moisture profiles obtained from X-ray analysis in a water absorption test (Roels and Carmeliet, 2006; Roels et al., 2003). As a result of these tests, very different permeability levels were detected in the two types of clay.