PE-AL-PE (Polyethylene Polyethylene) multilayer pipes, which are the best option for internal gas connections.  

The pipes provide the advantages of both metal and plastic pipe, combining the strength of metal with the longevity and durability of plastics.  Their high flexibility makes them very easy to install and because they are covered in polyethylene they have a high resistance to corrosion.  

BASIC STRUCTURE: the pipe is composed of 5 layers.  The internal and external layers are made of high-density polyethylene or medium-density polyethylene, which are bonded with an adhesive, to the aluminum layer.  Its aluminum interlayer is 100% gas/oxygen tight and is heavily welded in an overlapping fashion.  All layers are extruded in one pass.