This International Standard gives guidelines to the standards writer in selecting thermal-insulation material properties for standards used in building applications. These guidelines are not intended to prove the suitability of any particular product for any given application. When standards are established or existing specifications are revised on the basis of these guidelines, the performance characteristics in these guidelines should be translated into product requirements (specified values) in the International Standard for a product or application, together with appropriate test methods, which must be fulfilled at the time of delivery, in order to ensure that the product provides the performance requirements in service. This relationship between specified values for the product and the service performance characteristic of the product in use can be different for different insulating products, depending on the characteristic of the material (e.g. ageing or time-dependent behaviour). This International Standard applies only to prefabricated thermal-insulation products, i.e. manufactured mats and boards including any facings or coverings which may be present, although the basic characteristics may also be applied to other insulation products, e.g. in situ in systems or components, where appropriate. The International Standard covers only thermal-insulation products for use in buildings within normal climatic conditions. It does not cover insulation products for building services, e.g. plumbing and heating, nor insulation products for industrial use. Acoustic properties are not included in the properties given in this International Standard, although these may be additionally required for some fields of application.