The short answer
Both PEX and copper make reliable water supply pipe. PEX is flexible plastic tubing that needs fewer fittings, is easier to route through finished walls, and is somewhat more tolerant of freezing. Copper is rigid metal with a very long track record, handles heat well, and isn't affected by sunlight. For many repiping jobs, PEX costs less to install. The right choice depends on your home, local code, your water and your plumber's recommendation.
PEX vs. copper at a glance
| PEX | Copper | |
|---|---|---|
| What it is | Cross-linked polyethylene tubing | Rigid metal pipe |
| Installation | Bends around corners; long runs with few fittings; crimp, clamp, expansion or push-fit connections | Cut and joined with soldered, press or compression fittings at every turn |
| Through finished walls | Easier to fish through walls, so smaller openings are needed | Needs more access for straight runs and fittings |
| Freezing | Can stretch somewhat, so it's less likely to split; not freeze-proof | More likely to split when frozen |
| Corrosion | Doesn't corrode | Can develop pinhole leaks, especially with aggressive water |
| Sunlight | Degrades under UV light; must not be left exposed outdoors | Unaffected by sunlight |
| Heat | Rated for household hot water; manufacturers set limits near heat sources | Handles high heat well |
| Typical cost | Usually lower for materials and labor | Usually higher, and copper prices fluctuate |
Types of PEX and copper
PEX comes in three main types, named for how it's manufactured:
- PEX-A: the most flexible; often used with expansion fittings, and kinks can sometimes be reversed with heat
- PEX-B: very common; slightly stiffer, typically used with crimp or clamp rings
- PEX-C: less common in whole-house repiping
Copper supply pipe is graded by wall thickness:
- Type K: thickest; often used for underground water service lines
- Type L: medium; a common choice for interior supply lines
- Type M: thinnest; used in some residential interior work where code allows
Which handles freezing better?
PEX has an edge here: it can expand somewhat as water freezes inside it, so it's less likely to split than rigid copper. But it isn't freeze-proof. Fittings and connections can still fail, a frozen PEX line still cuts off your water, and repeated freezing isn't good for any pipe. In a cold climate like northern Illinois, whichever material you choose should be routed away from exterior walls and unheated spaces where possible, and insulated where it can't be. See our post on what temperature pipes freeze at for more.
Which lasts longer?
Both can last for decades when installed correctly. Copper's lifespan depends heavily on water chemistry: aggressive or acidic water can thin copper walls over time and cause the repeated pinhole leaks many owners of older homes know well. PEX doesn't corrode, but it must be protected from sunlight and installed within the manufacturer's limits for heat and fittings. Installation quality matters more than material for both.
Can PEX and copper be mixed?
Yes, and it's very common. Plumbers often repair a split section of copper by splicing in PEX using transition fittings, or replace part of a system in PEX while leaving sound copper in place. That flexibility is one reason PEX is popular for repairs after a freeze. If you need a split line fixed, we can connect you with a plumber for repair work after a burst pipe in Elmhurst.
Check local code and ask your plumber
Which materials are allowed, and how they must be installed, depends on the plumbing code your municipality enforces. A licensed plumber should confirm what's permitted where you live and pull any permit the job needs. If you're considering replacing old galvanized or failing copper pipe, our pipe replacement page explains when it makes sense and what the job involves. Recurring pinhole leaks are covered under water leak repair.