The variation of relative humidity (RH) inside buildings can affect several aspects relevant to the users. The hygroscopic inertia of a room moderates RH variations and will usually have a positive influence on its overall behaviour. An extensive laboratory work aiming the characterization of the moisture buffering capacity of interior finishing systems, the assessment of a room’s hygroscopic inertia index and the definition of a methodology to tie inertia to RH peak dampening on a daily basis, is presented. The MBV – “Moisture Buffer Value” was evaluated for gypsum based products combined with different coatings. This set of experiments provided an evaluation of the moisture buffer capacity of finishing systems. The assessment of hygroscopic inertia at room level was implemented using a flux chamber designed specifically for this experiment. This facility has a high control level of hygrothermal parameters, allowing for a systematic comparison of the effect of different elements on the RH moderation. The same type of finishing systems was used in these experiments as in MBV determination. A daily hygroscopic inertia index, Ih,d, was defined using MBV as a basis for the assessment of materials to the buffering capacity of a room. The correlation between that index and peak dampening is proved using the presented experimental results. A methodology for the practical application of the hygroscopic inertia is derived from that correlation. Key words: Moisture, Hygroscopic inertia, Experiments