ISO 22391-1:2009 specifies the general characteristics of piping systems made of polyethylene of raised temperature resistance (PE‑RT), Type I and polyethylene of raised temperature resistance (PE-RT), Type II intended to be used for hot and cold water installations within buildings for the conveyance of water, whether or not the water is intended for human consumption (domestic systems) and for heating systems, under specified design pressures and temperatures appropriate to the class of application.

ISO 22391-1:2009 covers a range of service conditions (classes of application), design pressures and pipe dimension classes, and also specifies test parameters and defines terms. In conjunction with the other parts of ISO 22391, it is applicable to PE-RT pipes, fittings, their joints and to joints having components of PE-RT, as well as of other plastics and non-plastics materials, respectively, used for hot and cold water installations.