Moisture in building materials, particularly in cultural heritage structures, can cause reduction of mechanical strength, decrease of indoor comfort and alteration of thermal properties, aesthetic decay, and even material loss. To non-invasively quantify moisture content in porous materials, Active Infrared Thermography was used. The method was applied in the laboratory on brick sample with different moisture contents, as well as on a reference stone sample with known thermophysical properties, to evaluate the thermal inertia as a function of water content using a comparative approach. A heat flux was applied to the sample using a lamp, and thermal inertia was derived from the absorbed heat, influenced by the material's absorption coefficient. An indirect optical calibration enables estimation of this coefficient without applying high-emissivity or high-absorption coatings, preserving the integrity of sensitive heritage materials.