Walk into any plumbing aisle and you'll see PEX labeled as PEX-A, PEX-B or PEX-C. All three are cross-linked polyethylene tubing, and all three are used for hot and cold water supply lines in homes across the US. The letters refer to how the tubing is cross-linked, and that difference affects how flexible the pipe is, which fittings and tools it works with, how it handles a kink, and what it costs.
This guide focuses on the two types you'll see most often, PEX-A and PEX-B, so you can pick the right pipe and connection system for your project.
What "cross-linked" means
Polyethylene on its own softens with heat and isn't strong enough for pressurized hot water. Cross-linking creates chemical bonds between the long polyethylene molecules, turning them into a three-dimensional network. That network gives PEX its resistance to heat, pressure and creep, while keeping it flexible.
The ASTM F876 standard requires a specified range of cross-linking for PEX tubing, whatever the method. So PEX-A, PEX-B and PEX-C are all "real" PEX that meets the same basic standard. In the US, PEX tubing that meets ASTM F876 and F877 typically carries the same standard pressure ratings: 160 psi at 73°F, 100 psi at 180°F and 80 psi at 200°F. Check the print line on the tubing for its exact ratings and listings.
How PEX-A is made: the Engel (peroxide) method
PEX-A is cross-linked using the Engel method, also called the peroxide method. Peroxide is mixed into the polyethylene, and cross-linking happens while the material is hot, during or right after extrusion. Because it occurs while the polymer is still in a molten state, PEX-A typically reaches the highest degree of cross-linking of the three types, often cited at around 85%.
The result is a pipe that's noticeably softer and more flexible, with a strong "thermal memory": when heated, it tries to return to its original shape. That property is the basis of cold-expansion fittings and heat-gun kink repair, covered below.
How PEX-B is made: the silane (moisture-cure) method
PEX-B uses the silane method. A silane compound is grafted onto the polyethylene, the tubing is extruded, and cross-linking happens afterward when the pipe is exposed to heat and moisture (for example in a steam or hot water bath). PEX-B typically reaches a cross-linking level of around 65% to 70%.
PEX-B is stiffer than PEX-A and has less thermal memory. It's widely used for residential water lines and is common in big-box retail.
What about PEX-C? PEX-C is cross-linked after extrusion by electron-beam radiation. It sits between A and B in flexibility for many products, and it's usually joined with crimp or clamp fittings.
Flexibility and handling
- PEX-A is the most flexible. It makes tighter bends with fewer fittings and uncoils more easily, which helps in cold weather and in tight framing. A tighter bend radius means fewer elbows and fewer connections that could leak.
- PEX-B is stiffer and has more coil memory, so it tends to spring back toward its coiled shape. It needs a larger bend radius, and bend supports or 90° fittings are used more often. Some installers like that stiffness for long, straight runs that look neater.
Always follow the tubing manufacturer's minimum bend radius. Bending tighter than allowed can kink the pipe.
Fittings: expansion vs crimp and clamp
The fitting system is the most practical difference between PEX-A and PEX-B, because it determines which tools you need.
| Connection | Standard | How it works | Typical tubing |
|---|---|---|---|
| Cold expansion with PEX ring | ASTM F1960 | An expansion tool stretches the pipe end and a PEX ring. The fitting is inserted, and the pipe shrinks back around it. | PEX-A |
| Copper crimp ring | ASTM F1807 (metal insert) / F2159 (plastic insert) | An insert fitting goes into the pipe, and a copper ring is compressed with a crimp tool. | PEX-B, PEX-C, and many PEX-A tubes |
| Stainless steel clamp (cinch) ring | ASTM F1807 / F2159 fittings with F2098 rings | A stainless band is cinched over an insert fitting with a ratcheting clamp tool. | PEX-B, PEX-C, and many PEX-A tubes |
| Push-to-connect | ASSE 1061 | The pipe pushes into a fitting with an internal grip ring and O-ring. No tool needed beyond a cutter and deburr tool. | All types listed by the fitting maker |
Expansion (F1960) fittings
Expansion fittings rely on PEX-A's thermal memory. After the pipe is expanded over the fitting, it shrinks back and grips tightly. Expansion joints are popular with professionals because the pipe is expanded rather than squeezed, so the fitting's inside diameter can be larger than a crimp fitting of the same size, which means less flow restriction. A joint made in cold weather takes longer to shrink down, so give it time before pressure testing.
Standard F1960 expansion fittings are generally intended for PEX-A only. PEX-B doesn't have enough memory to shrink reliably around them. A few manufacturers offer their own expansion systems for PEX-B, but those use specific rings and fittings from that maker. Never mix systems unless the manufacturer lists them as compatible.
Crimp and clamp fittings
Crimp and clamp fittings work on PEX-B and PEX-C, and many PEX-A tubes are also listed for them. Check the print line on your tubing for the ASTM standards it's listed with. Crimp tools must be sized and calibrated for the ring, and every connection should be checked with a go/no-go gauge. Clamp (cinch) tools usually cover several sizes with one tool and release automatically when the clamp is complete.
Shop insert fittings in our PEX crimp fittings (F1807) collection, or browse the full range of PEX fittings.
Cost
Prices change, but some general patterns hold:
- Tubing: PEX-B is usually less expensive per foot than PEX-A.
- Tools: Crimp and clamp tools generally cost much less than a PEX expansion tool, especially a battery-powered one. For a small DIY repair, the tool cost often decides the choice.
- Labor and fittings: For a whole-house repipe, PEX-A's flexibility can reduce the number of fittings and speed up installation, which offsets some of the material cost for professionals.
See our PEX tools for cutters, crimpers, clamp tools and expansion tools.
Kink repair
Kinks happen, especially when you uncoil tubing in a hurry. Here PEX-A has a real advantage:
- PEX-A: Many PEX-A manufacturers allow kinked tubing to be repaired with a heat gun. Warm the kinked section evenly, and the pipe's thermal memory returns it to its original round shape. Follow the manufacturer's procedure. Never use an open flame, and don't overheat the pipe.
- PEX-B: A kink in PEX-B generally can't be heat-repaired. Cut out the damaged section and install a coupling.
Other considerations
- UV exposure: All PEX is damaged by sunlight. Store it out of the sun, and follow the manufacturer's maximum UV exposure time. Don't install it where it's exposed to sunlight.
- Heat sources: Keep PEX away from flue pipes, recessed lights and other high-heat sources. Many manufacturers and codes require a metal connector or a minimum distance (often 18 inches) at a gas water heater's connections.
- Freeze tolerance: PEX is more forgiving than rigid pipe when water freezes, but it can still split. Insulate or protect lines in unheated spaces.
- Codes: PEX is accepted by the major US plumbing codes, but local rules vary. Check with your local building department.
PEX-A vs PEX-B: quick comparison
| PEX-A | PEX-B | |
|---|---|---|
| Cross-linking method | Engel (peroxide), during extrusion | Silane (moisture cure), after extrusion |
| Typical cross-link level | About 85% | About 65–70% |
| Flexibility | Most flexible, tight bends | Stiffer, more coil memory |
| Main fitting system | F1960 expansion (also crimp/clamp if listed) | Crimp or clamp (F1807 / F2159) |
| Kink repair | Heat gun, per manufacturer | Cut out and couple |
| Typical cost | Higher tubing and tool cost | Lower tubing and tool cost |
Which should you choose?
- Choose PEX-A if you're doing a larger project or repipe, want the most flexible tubing, prefer expansion fittings with less flow restriction, or want the option of heat-repairing kinks.
- Choose PEX-B if you're making repairs or a smaller project, want lower tubing and tool cost, or already own a crimp or clamp tool.
- Either way: Use one connection system consistently, with tubing, fittings and rings that are listed together, and pressure test before closing up walls.
Browse PEX pipe and tubing in both types, in a range of sizes and colors. Need help matching tubing to fittings? Send us the print line from your existing pipe and we'll help you find compatible parts.