Walls made by Fiorditufo blocks present not only a high thermical isolation but also an excellent ability of perspiration of water vapour. The resistance factor of the diffusion of water vapour (μ), is quite low, between 11 and 12, according to UNI 9233 and DIN 52615. The ability of perspiration is equal to the ability of a pozzolanic plastering or of the recent cement-air-mortars, that are used for the curing of humid walls. Consequently a wall made by Fiorditufo blocks is able to dry quickly by itself, if it takes humidity. Its great capacity to absorb 30% (and more) of water allows a drastic reduction of the phenomenon of condensing in places with a strong presence of vapour. The tuff-stone is able to absorb easily the condensing that is generating on the walls and avoids the coming-up of water drops on the surface that would lead to mildew and bacterial proliferation.