Foamed plastic insulations installed into buildings are now expected to be long-lasting materials. However, in recent years, it has been reported that the foamed plastic insulation installed in the high-humid environment, such as under waterproof sheets on a rooftop, absorbs moisture and subsequently increases the thermal conductivity. The mechanism of moisture absorption is not sufficiently clear, and the test method for thermal conductivity of building insulating materials does not consider the influence of humidity. This study observed both moisture absorption and changes of physical properties of foamed plastic insulations after exposed at high humidity and discussed the moisture-induced deterioration.
