The PEX pipe distribution box, often called a plumbing or heating manifold, is central to modern radiant floor heating and plumbing systems. Its market growth is intrinsically linked to broader trends in construction and sustainable technology. This Guide is a joint industry publication from The Plastics Pipe Institute (PPI), The Plastic Pipe and Fittings Association (PPFA), Home Innovation Research Labs (HIRL), with support from IAPMO and ICC. It provides information and resources necessary to design and install crosslinked polyethylene. Uponor has used reasonable efforts in collecting, preparing, and providing quality information and material in this manual. However, system enhancements may result in modification of features or specifications without notice. Uponor is not liable for installation practices that deviate from this. ong with their recommended installation method. Wavin Pex pipes and fittings present numerous advantages over rigid pipe systems, including superior fle astructure industry across multiple continents. Backed by 60+ years of expertise, we are geared up to tackle some of the world's biggest. Cross-linked polyethylene (PEX) is a high-temperature, flexible, polymer pipe. Cross-linking technology was first developed in Europe and has since come into use around the world for a variety of applications.