What is PEX?

About PEX pipes

PEX stands for Cross-linked polyethylene, a flexible plastic-like material used for water pipes. It is increasingly becoming a more and more common building material for water pipes. 

It should NOT be confused with Polybutylene, a gray plastic-like pipe material that was known for a high rate of failure. 


PEX was developed in Germany in the late 1960s’. In the 1980s, it became widespread across Europe as an alternative to copper and galvanized steel as a water pipe material. It was slowly introduced to the United States in the 1980s, though it was slow to be adopted.

The state of California officially approved PEX as a code-compliant material in 2009, and is listed as an approved material in the California Plumbing Code section 604.01. However, various jurisdictions, particularly Santa Clarita, had adopted its use much earlier. The City of Los Angeles officially approved PEX in a memo dated April 22, 2013. Despite being legal, in many areas, PEX remained uncommon until approximately 2019.


Pex is commonly seen in red and blue, though it can also be found in white and other colors. Plumbers commonly use blue for cold water and red for hot water in a house, although there is no difference in the material. The use of colors is simply to stay organized.

Pex Plumbing
Pex Plumbing under a home


Lower cost of materials

The main issue with copper piping is the constant rising prices of raw copper. Similar to silver and gold, copper prices rise and fall with the market. And while there have been a few dips in the market, such as in the year 2000, in general, the price of copper has significantly risen in the last 20 years. PEX is simply a more cost-effective material.

Lower Cost to Install

The other issue is copper requires welding or soldering pieces together, particularly at corners. This presents additional costs and welding comes with certain safety hazards. Every run of pipe and joint has to be planned out.

You’ll often see in homes burn marks on wood where the plumber was soldering copper joints. And any solder that isn’t perfect can be a source of future leaks.

Whereas PEX is flexible and easily bends, making it relatively easy to install. A plumber can simply run a line, cut off any excess, and not worry about multiple connections.

No one steals PEX from the job site

A big issue with copper piping is theft. Regardless if it is a big multi-house project, or a single home being renovated, builders have to guard against copper theft. It has become all too common for thieves to break into a house under construction at night and steal all the copper pipes and then resell them to scrap yards. This is because, as mentioned, the rising prices of copper make scrap copper an attractive material to steal. Whereas PEX has no real resale value.

PEX does not corrode or hammer.

Galvanized steel was a popular choice for water piping up through the late 1960s and was used in some places like Palmdale and Lancaster up until the early 1980s. Galvanized steel has largely been abandoned as a pipe material because it corrodes easily and does not last. Copper does not corrode as easily, but it still can corrode. One of the biggest issues with copper is if it comes in contact with any other metal, this causes electrolysis or an electrochemical reaction. Any contact with a metal pipe hanger, a nail, or any contact with a galvanized pipe can cause significant deterioration of a copper pipe. Other issues with copper pipes may be caused by a water supply that is either too high or low on PH, traces of other metal minerals, among other issues that can slowly corrode copper over time. 

Copper pipes can also hammer, where it sounds like someone in the wall is hammering to get out when a faucet is turned on. This is caused by pipes that move in the walls when the water pressure changes. Hammering can be very loud, and annoying, although it is fixable.

PEX simply does not have these issues



PEX can not be exposed to direct sunlight for long periods of time. The material will break down from natural ultraviolet rays. When installed in an attic, in walls, and under a house, this is usually not a problem. But if the PEX is too close to an attic or cralwspace vent, it can become an issue. PEX can not be used outdoors under any circumstances.

PEX installed near a window
PEX installed near a window


While PEX can not corrode like copper or galvanized pipes, metal still has one big advantage over PEX. Rodents can not chew through a metal pipe. However, a rodent can chew through a PEX pipe. If a rodent were to get into a home and chew through a PEX pipe, the pipe will leak and create a mess.

Bad Fittings

While PEX itself is a plastic-like material, it is sometimes installed with brass fittings. Some early brass fittings failed. Some brass fittings can give out over time for similar reasons as copper, ie they are affected by water quality, and/or just were never installed correctly to being with. A defective fitting may not present itself as defective for many years after it was installed.

PEX pipe with brass fittings
PEX pipe with brass fittings

PEX is semi-permeable

PEX is a semi-permable material. Meaning other liquids can leach into the pipe. This can be a problem if say a PEX pipe were to come in contact with a broken sewage pipe. Or if a can of gasoline or paint thinner was to be accidentally spilled onto a PEX pipe, water in the pipe could become contaminated.

PEX is not approved for a few things

PEX can not be within 6″ of the water heater. The first 6 inches of piping coming in and out of the water heater should be metal. A water heaters temperature relief valve should not use PEX.  Only water supply pipes are approved to be PEX, not drain pipes.

PEX is here to stay

While there is some minor debate over if PEX is the best material for water pipes, the consensus is it is here to stay. Almost all new constructions homes in California built since 2019 that we inspect appear to have been built with PEX. Even higher-end luxury homes are using PEX to save building costs. 

More and more re-piping jobs of older homes are being down with PEX rather than copper. We used to only see PEX in the Santa Clarita area, we now see PEX throughout the greater Los Angeles area. Copper prices and the extra labor needed to install copper have made PEX the preferred water pipe material of most home builders, home remodelers, and plumbers across Southern California.

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