Modern Japanese houses are thermally insulated and airtight. However, as the climate is hot and humid, problems relating to condensation have increased. To solve these problems, building materials are being developed that can control humidity. The microporosity of the wall material is closely related to humidity absorption, thus by utilising porous materials and low firing temperatures it is possible to obtain materials with excellent humidity absorption and release properties in addition to good strength and other physical properties. The frequency of dew formation is then reduced considerably and air pollution is reduced. By comparison to air conditioning systems, no external energy is consumed. ECO-CARAT, developed by the INAX Corp., is a wall finishing material capable of self-controlling room humidity and air quality. It is pioneering a new trend in the development of interior finishing materials. The characteristics of ECO-CARAT, which is made from allophane, a porous clay mineral originating from volcanic ash, are described. 3 refs.