Multilayer pipe or PAP is an integrated system of cross-linked polyethylene pipes with an aluminum core (PE / Al / PE-X). The tube can be used for the supply of hot and cold water in plumbing installations, heating "Radiator (heating)") and underfloor heating.

The tube is of hybrid construction, metal and thermoplastic, made up of three structural layers: polyethylene (PE), aluminum (Al) and polyethylene (PE), and two intermediate adhesive layers to hold the whole together.