This European Standard specifies the equipment and procedures for determining the water vapour transmission rate, water vapour permeance and water vapour permeability of test specimens in the steady state. These properties can be determined under different sets of specified conditions. It is applicable to thermal insulating products. This standard is applicable for homogeneous materials and for products which may contain integral skins or facings of different material(s). A material is considered to be homogeneous, with regard to mass distribution, if its density is approximately the same throughout, that is, if the measured density values are close to its mean density. This test method is not normally used for determining the water vapour transmission properties of single, separate vapour barriers (of high diffusion resistance), such as prefabricated films, foils, membranes or sheets, due to the long duration of the test. For products with a vapour retarder or barrier with a water vapour diffusion equivalent air layer thickness sd ≥ 1 000 m other test methods (for example, IR-detection) can be used for measuring the single separate vapour retarder or barrier, provided that the results obtained are in the same range as the values measured in accordance with this standard. The water vapour transmission rate and permeance values are specific to the test specimen, that is, the product thickness tested. For homogeneous products, the water vapour permeability is a property of the material. The committee responsible for this standard is NA 005-56-60 AA "Wärmedämmstoffe (SpA zu CEN/TC 88 und WG 1 bis 9, WG 12 bis 21, ISO/TC 61/SC 10, ISO/TC 163 (partly), ISO/TC 163/SC 1 und SC 3)" ("Thermal insulation materials (mirror committee for CEN/TC 88 and WGs 1 to WG 9, WGs 12 to 21, ISO/TC 61/SC 10, ISO/TC 163 (partly), ISO/TC 163/SC 1 and SC 3")) at DIN.