PEX pipe is flexible plastic tubing in red, blue, or white, with size markings on the side and smooth ends for crimp, clamp, or expansion.
Why this question matters
Spotting PEX fast saves time on repairs, upgrades, and quotes. If you know what the tubing looks like, you can tell hot from cold lines, separate potable runs from heating loops, and pick fittings that actually fit. This guide gives you a clear picture of PEX so you can ID it without guesswork.
Quick visual id table
| Feature | What you’ll see | Why it helps |
|---|---|---|
| Color | Red for hot, blue for cold, white or natural for either | Faster tracing of runs across a home |
| Flex | Coils and sweeping curves around corners | Fewer elbows and joints in view |
| Print line | Size, SDR9, ASTM, NSF marks printed repeatedly | Confirms type and drinking water listing |
| Finish | Semi-gloss plastic look; no glue seams | Distinguishes PEX from glued PVC or CPVC |
| Ends | Clean, round ends ready for rings or sleeves | Signals crimp, clamp, push, or expansion fit |
| Barrier clue | Text like “oxygen barrier” or a thin outer layer | Points to radiant or boiler circuits |
| Composite clue | Stiffer tube that holds a shape, often orange | Usually PEX-AL-PEX for heating |
Colors, sheen, and the telltale print line
Most potable lines use red and blue for easy tracing, while white or natural works for either temperature. The surface looks like smooth plastic with a slight sheen. The strongest giveaway is the repeating print line: brand, nominal size, SDR9, a standard such as ASTM F876 or F877, and a health mark like NSF-61 or NSF pw. If you can read those stamps, you can confirm you are holding potable PEX, not a look-alike.
Tubing size is outside-diameter based, and the wall is thick compared with same-nominal copper. That is why a half-inch PEX line looks beefier than a half-inch copper tube. If the wall shows a faint extra skin or the text includes words like oxygen barrier, it is meant for hydronic loops where oxygen diffusion needs control.
Coils, straight sticks, and bend radius
In basements and crawl spaces you will often see big coils feeding a manifold, then long sweeping arcs to fixtures. On open walls, some installers switch to straight 10- or 20-foot sticks to keep lines tidy. PEX makes wide turns without kinks when the bend is gentle; sharp bends need a plastic elbow or a bend guide.
Those soft curves are a clear clue you are not dealing with copper or CPVC. The line will spring when you move it, then settle into place again. That springy feel is normal and helps the tube ride through studs and joists without many fittings.
Minimum bend tips
A tight turn compresses the inside wall and can leave a flat spot. Give the tube a broad arc and use a bend insert or an elbow when space is tight. When a kink does appear, a careful heat fix can round it back out on many brands, though badly creased spots deserve a short replacement piece.
Type a, b, c: what the letter means to your eyes
The letter refers to how the polymer chain was crosslinked at the factory, not a grade. PEX-a tends to be the most flexible and is common with expansion fittings. PEX-b is widely used and often found in big box coils and sticks. PEX-c shows up as well and looks the same to most eyes. All three carry the same basic print line data when listed for potable service.
If you see oversized plastic sleeves or rings on the ends, that hints at an expansion system usually paired with PEX-a. If you see copper rings or stainless clamps squeezed on a black or brass fitting, that points to crimp or clamp systems that any listed PEX type can use.
Oxygen barrier and pex-al-pex cues
Barrier PEX adds a thin outer layer that slows oxygen from getting through the wall, which protects cast iron and steel parts in heating loops. Many brands label this right on the print line. The color often skews white, gray, or orange, but color alone is not proof.
PEX-AL-PEX is a different animal: two plastic layers with a bonded aluminum core. It bends and stays put with less springback, and many rolls come in orange. You may see the seam of the core if you look closely at a cut end. This product is common in radiant heat, baseboard runs, and snow-melt circuits.
Fittings that match the look
Next to the tube, you will spot matching hardware. Crimp systems use copper rings pressed over brass or polymer fittings. Clamp systems use a stainless cinch band with a small ear. Push fittings have a wider body and a release collar. Expansion systems show a plastic ring that was stretched to slide over the fitting, then shrunk tight.
Each system makes a different silhouette at the joint. That silhouette is another way to confirm the line is PEX and to plan the tool you need if you are adding a tee or a shutoff.
Where you will see pex in a home
Near the water heater or boiler, look for a small distribution panel with many takeoffs. That is a manifold, and it pairs well with PEX. Tracer colors and labels help you follow each branch to a bath or kitchen.
In framed walls, the tube snakes through holes in studs with plastic nail plates at risky spots. Under floors, it hugs joists and hangs on plastic or metal straps. At fixtures, it often ends at a stub-out elbow or a straight stop with a push fitting or a crimped adapter.
What pex pipe looks like next to copper or pvc
Copper is rigid, shiny, and joined with soldered fittings or press sleeves. CPVC is rigid plastic in cream or light yellow with glued sockets and printed primer at joints. PEX is flexible and shows long arcs between holders with mechanical rings or sleeves at joints. You rarely see primer stains at a PEX joint, and you rarely see perfect right angles unless the installer used formed elbows.
Another cue is noise. When a faucet closes fast, PEX tends to quiet the water hammer that echoes through rigid lines. The tube also resists dents and pinholes that would stand out on old copper.
How to read the print line
Scan for three groups of text. First, standards such as ASTM F876 or F877 that set dimensions, material requirements, and pressure ratings. Second, health marks such as NSF/ANSI/CAN 61 or “NSF pw,” which indicate potable listing. Third, the size and SDR9, which ties to the outside diameter used by fittings. If any required stamps are missing, treat the tube as non-potable for plumbing.
Common stamps you will spot
Look for the brand name, a date code, and sometimes a short UV digit that hints at storage limits in sunlight. Many rolls also include a footage mark every few feet, handy when pulling long runs to a bath group.
Some brands also print usage tags like “oxygen barrier” for hydronic service. Others include a code letter that hints at UV resistance during storage. If a shed window leaves the coil in sun for weeks, the wall can chalk or turn brittle, so storage out of direct sun is smart practice.
Code, storage, and safe handling cues you can see
Listed PEX for drinking water carries the marks above and appears in many model codes. For a deeper reference, the PPI PEX design guide shows typical layouts, hanger spacing, and joint options used in typical homes.
Sunlight can age the wall when exposure drags on, so you will often see coils shipped in bags or boxes, and installers tuck runs away from windows. Near heaters, look for a short metal connector or a listed transition fitting to manage heat right at the appliance stub.
Common pex flavors you will spot
| Type | Visual clue | Where it shows up |
|---|---|---|
| PEX-a | Works with expansion sleeves; tightest bend | New builds with expansion tools |
| PEX-b | Often sold in red, blue, white coils and sticks | Remodels and tract work |
| PEX-c | Looks like other PEX; check print line | General plumbing |
| Barrier PEX | “Oxygen barrier” on print or faint outer skin | Hydronic heat |
| PEX-AL-PEX | Holds shape; orange or white common | Radiant and baseboard loops |
Manifolds, stubs, and sizing cues
A manifold looks like a slim panel with many shutoffs and labels. Each takeoff feeds a single sink, shower, or appliance. Near fixtures you may see a short copper or brass stub coming through the wall with a stop valve; the PEX connects behind that plate with a crimp, clamp, or push joint.
Nominal sizes echo copper terms, but the outside diameter tells you which fitting to pick. A half-inch PEX line uses the CTS family of fittings sized to the outside, not the inside. When in doubt, read the print line and carry a gauge.
Simple checks before you cut
Wipe a dusty section and read the stamps. If they repeat every foot or so, take a quick photo for later. Trace color back to the source to spot a manifold or a mixing valve. At a joint, study the ring: a full copper band with a single crimp dimple points to a crimp tool; a band with a small raised ear points to a cinch tool; a thick plastic ring points to expansion.
Look for kinks. Minor ones that were reshaped with heat will show a faint white crease yet still feel round. Bad kinks stay flattened; those sections should be replaced with a coupling.
What pex pipe looks like in real installs
In a retrofit, you might see PEX jump from old copper near the meter, run along joists, then split to a bath group. In a new build, you will likely find neat bundles fanning from a central manifold, each with color-coded lines and labels. Both scenes share the same core look: flexible SDR9 tubing, clear print lines, and joints made with rings or sleeves instead of solvent glue or solder.
Pictures online often show bright showroom coils. Real houses add dust, straps, and tight turns around framing. Use the print line and the joint hardware as your north star and you will nail the ID every time.
What does pex tubing look like behind walls
Behind drywall, expect gentle arcs through notched or drilled studs with nail plates where needed. The tube sits on plastic insulators or hangers to reduce rub noise. When it passes a tub or shower, it hits a valve with crimped or clamped joints and then heads up to the head or down to a spout with the same joint style.
At a toilet, a blue or white line runs to a quarter-turn stop, then a short braided connector finishes the trip. Under a sink, red and blue lines hit angle stops or a small manifold feeding a faucet, dishwasher, or filter.
Visual red flags to watch for
Long sun exposure leaves a chalky surface and brittle feel; replace those runs. Burned or scorched patches near a flue or heater need attention and a safe metal transition. Corroded brass fittings or green crust at a joint call for a new coupling, and dark rings can signal a bad crimp or a water reaction.
Hangers matter too. Lines that sag between hangers or rub on sharp metal plates can wear. Add listed hangers and guards so the tube keeps its round shape and smooth surface.
Practical points you can use on site today
PEX looks like flexible plastic tubing with bold print lines and clean mechanical joints. Colors help trace hot and cold, while stamps confirm size, listing, and intended use. Barrier versions and PEX-AL-PEX add small visual twists that point to heating work.
Read the wall, read the ring, read the print. With those three checks, you will spot PEX quickly and pick fittings that work the first time. That keeps jobs tidy.