PEX-a is made using the Engel method or high temperature peroxide method. The Engel method is a hot cross-linking process, meaning the actual cross-linking takes place during the extrusion process when the base polyethylene is above its crystal melting temperature, through the introduction of peroxide to break the polyethylene chains. The Engel method provides more precise control over the degree, consistency and uniformity of cross-linking. This means the tubing is evenly cross-linked, with no weak links within its molecular chains. In a PEX-a pipe, the polyethylene chains are linked directly through a double carbon-carbon covalent bond.
This is the most flexible type of PEX pipe with 5-6x outside diameter bend radius.
Compatible connection types with PEX-a are: ASTM F1807, F1960, F2080 & F2159
PEX-B is made using the Silane (or moisture cure) method. This method performs the crosslinking after extrusion with a silane chemical agent and accelerated using heat and moisture. This bridge crosslinking inserts a silane bridge molecule between two polyethylene chains, similar to vulcanization of rubber, and results in a much stiffer final product than PEX-a, with lower workability and typically 8x outside diameter bend radius.
Typically, ASTM F1807 connection types are used with PEX-b, though some (e.g LegendFlex) are also compatible with expansion type fittings. To be sure which fittings are certified for use with your pipe, check the print stream.
PEX-c is manufactured using the irradiation method of cross-linking and is often called the “clean method” as it does not use any chemical byproducts in the crosslinking process. This was the first method of crosslinking, used for cable jacketing as far back as the 1950s. With the Irradiation method the pipe is extruded first and then passed through an electron beam to complete the cross-linking. The Irradiation method provides more precise control over the degree, consistency and uniformity of cross-linking. This means the tubing is evenly cross-linked, with no weak links within its molecular chains. PEX-c has an identical molecular structure as PEX-a pipe, with the polyethylene chains linked directly through a double carbon-carbon covalent bond.
PEX-c is flexible, expandable and has thermal memory (kink repair ability) with typically 6x outside diameter bend radius
Compatible connection types with PEX-c are: ASTM F1807, F1960, F2080 & F2159
PEX-D (also called PEX-other) is produced using the azo crosslinking method, with azobenzene stimulating the molecular graft, giving a similar molecular structure to PEX-b. There are currently no commercially available PEX-D products with approval for potable water use in North America.
PE-RT is an acronym meaning polyethylene for raised temperature. PERT shares many of the physical properties of PEX pipe (including the same base plastic, polyethylene) and can be used in many of the same plumbing and hydronic heating applications. This plastic has been in use in Europe for over 35 years and is slowly being adopted into North American plumbing codes for domestic use. If you are unsure of whether PE-RT is approved for use in your jurisdiction, be sure to check your local code before installation.
PE-RT is extremely flexible at above freezing temperatures, typically with a 5-6x outside diameter bend radius.
Is a multi-layer pipe made of two PEX layers with a continually laser welded aluminum layer in the center. The aluminum layer is bonded to the PEX layers with a special adhesive material. This combination of special raw materials of very high molecular weight result in a special pipe having several important qualities; corrosion resistance, excellent mechanical resistance, lower expansion rate, unique chemical resistance, very low friction coefficient, no oxygen permeation, and high working pressure and temperature. It is important to note that PEX-AL-PEX requires special fittings and is not compatible with standard pex fittings of crimp or expansion style.
Flexible and it will keep its shape due to aluminum core.