# 2004 Milan
The development of a new family of PE materials with significantly improved processability and long term strength at high temperatures is discussed. These polymers form the basis for a new ISO class of polyethylene materials : PE-RT (Polyethylene of Raised Temperature resistance) for hot and cold water pipe applications. These materials have a unique molecular structure and crystalline microstructure, which provides excellent Long Term Hydrostatic Strength at high temperature without crosslinking the material. PE-RT type materials are successfully used in domestic hot and cold water piping systems for all applications. These materials provide significant process advantages to the converters, allowing high line speed pipe production. The first member of the PE-RT family is targeted at the heating pipe market (covered by ISO 10508 classes 4 and 5), providing excellent flexibility and ease of installation to the installer. A recently developed PE-RT type material offers still higher long-term strength at high temperature and further improved processability. This combination makes this resin particularly suitable for all-plastic plumbing pipe (class 1 & 2 of ISO 10508) and thin wall, high line speed extrusion. An example of the latter is in metal/plastic composite pipes. Pipes based on these materials can be connected via heat welding or by the use of mechanical fittings. This paper presents the material science and product design concepts that govern the high long-term hydrostatic strength at high temperatures. By controlling the molecular structure, the melt rheology and solid state properties can be influenced. This results in a unique balance of processability and hydrostatic strength. Further discussed are the product features and benefits of PE-RT materials. The paper shows examples of the application range for this type of products.