According to previous existing studies, the building materials can have a high impact on relative humidity fluctuations in a room by adsorption/desorption processes. The aim of this paper is focused to determine the influence of commonly used furniture materials to indoor air relative humidity. The measurements were performed in a controlled environment of the climatic chamber. During the measurements, a stable indoor temperature together with a constant air moistening was ensured. The indoor air parameters were measured with data loggers as well as the periodical weighting of materials was performed, to determine the moisture content of materials. The results showed that the common furniture materials have a very significant impact on indoor air relative humidity. The calculations of the influence were performed according to the mass balance equation comparing the predicted results without considering the influence of materials to the actual measured results from real case studies, therefore estimating the adsorption capabilities of these materials. The influence of these materials to the stabilization of indoor relative humidity can be expressed as a coefficient in mass balance equation depending on the type of material, area, and thickness of material, initial moisture content, and indoor air parameters. The findings of these results can be used in the design stage of indoor climatic systems to more precisely predict the relative humidity.