PEX A vs PEX B: Differences, Fittings and Which to Use

The difference between PEX-A and PEX-B is how the pipe is cross-linked and, in practice, which fittings it takes. PEX-A (peroxide, or Engel, method) is the pipe for cold-expansion fittings. PEX-B (silane, or moisture-cure, method) is usually joined with crimp, clamp, press or push-to-connect fittings. Both are built to ASTM F876 and sold for drinking water, and the letter names a manufacturing method, not a quality grade.

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The short answer

This page is built from maker documents (Uponor, Viega, Zurn, SharkBite, REHAU, Apollo) and from ASTM and Plastics Pipe Institute (PPI) summaries. Nothing here comes from our own testing. Most makers favor the type they sell, so their claims are attributed, and where they disagree I say so. Maker pages read September 29, 2026.

Related: brass or poly fittings, PEX expansion tools for the PEX-A route, and the PEX cutter guide for a square cut before any joint.

PEX-A vs PEX-B at a glance

What the letters mean

A, B and C are not quality grades and not brands. They name how the polyethylene is cross-linked. Cross-linking improves temperature resistance, strength and flexibility, according to Viega.

• PEX-A: peroxide, or Engel, method (SharkBite). Uponor quotes 80% cross-linking or more.
• PEX-B: silane, or moisture-cure, method (SharkBite). Uponor quotes 65 to 70%. SharkBite calls it the most common type.
• PEX-C: electron-beam irradiation. Uponor quotes 70 to 75%. SharkBite says it is commonly used for supply lines from the stop to the fixture.

The standard both are built to, ASTM F876, names the tests every PEX tube must pass: dimensions, density, sustained pressure, burst pressure, environmental stress cracking, degree of crosslinking, stabilizer functionality and oxidative stability in chlorinated water. It also covers UV resistance. Tube size is the same across the letters: SharkBite says all PEX is copper tube size. ASTM F877 covers the tube and fittings together as a system.

Where the makers disagree

• Uponor (sells PEX-a): says PEX-a is better in kink repair, bend radius, stress-crack resistance and freeze/thaw resiliency, and links that to higher cross-linking.
• Viega (sells PEX-B): says the letters “have nothing to do with quality or performance,” and warns not to assume every PEX-A is more flexible than every PEX-B.
• SharkBite (sells both): says the differences in density, burst pressure and bend radius between types are negligible.

All three are selling something. The safe reading: the letter tells you the process, and the spec sheet for the exact product tells you the performance.

Which fittings go with which pipe

This is the real decision. SharkBite puts it plainly: tubing is marked with the standard designations for the fitting systems approved for use with it, so check the pipe. Viega adds that press and expansion fittings are not interchangeable, and that each method depends on an approved combination of tube, fitting, ring or sleeve, and tool.

Two notes on that table. First, Zurn says its PEX-B, made with a variation of the silane method, works with both F1807 crimp and F1960 expansion fittings, and that certified tool heads exist for it. That is why “PEX-A takes expansion, PEX-B takes crimp” is the usual pattern, not a universal rule. Second, if you are choosing between the two ring systems, we compare them in PEX crimp vs clamp. Starting from nothing, a PEX tubing and fittings starter kit is a common way to begin.

Insert fittings and flow

Crimp and clamp fittings have a barbed body that sits inside the tube, so each joint narrows the bore a little. SharkBite says an expansion fitting’s internal diameter is closer to the pipe’s, which can help maintain flow. On a short run this is a non-issue. On a long run with many elbows and tees, especially if you are already fighting low water pressure, it is a fair argument for expansion fittings or for one size larger on the trunk. The size-up idea is my rule of thumb, not a maker rating.

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Tools: what each system needs

I am not quoting tool prices, because they move. Viega makes the fair point that the lowest tool price does not always give the lowest installed cost, so count heads, jaws, rings and battery platforms too.

• Expansion (PEX-A): an expansion tool with a head for each pipe size, plus rings. Uponor says ProPEX joints need no torch, glue or gauge and cannot be dry fit. Zurn says its F1960 expansion head fits DeWalt DCE400 and Milwaukee M12 ProPEX tools, so heads are not always brand-locked. Compare cordless tools in DeWalt vs Milwaukee PEX expander.
• Crimp: a crimp tool sized to the ring, and a go/no-go gauge to check each joint. SharkBite says crimp joints are typically verified with a go/no-go gauge, and ASTM F2159 carries a GO/NO-GO gauge appendix. Tool choices are in the crimp and cinch tool guide, and a leaking joint is covered in PEX crimp fitting leaking.
• Clamp (cinch): a clamp tool. ASTM F2098 covers the stainless clamps as an alternative to copper crimp rings. If a ring goes on wrong, see how to remove a PEX crimp ring.
• Press: a press tool. SharkBite says its PEX press fittings work with commonly used press tools whose jaws meet ASTM F3347 and F3348, on either type, can be tested right away and cannot be disconnected after installation.
• Push-to-connect: no special tool. SharkBite lists it as best for service, repair and remodel work, and says it can be removed. For a tight repair, see our push-to-connect fittings guide.

Kinks and tight bends

Makers split on this one. Uponor says its PEX-a has thermal memory: warm a kink with a heat gun and it returns to round, and it adds that this works only on PEX-a. Zurn agrees that a kinked PEX-B section has to be replaced. Viega says heat repair is possible on some products, but it is slow, the tube tends to kink again in the same spot, and cutting out the kink and adding a fitting is more reliable and keeps its warranty coverage in place.

Bend radius is the other half. Uponor lists the minimum bend radius of its PEX at six times the outside diameter. Other makers publish their own numbers, and Viega says not to assume every PEX-A bends tighter than every PEX-B. Compare the spec sheet for the exact tube. In open basement runs none of this matters much. In tight joist bays and stud cavities it matters more, because a kink means fishing the line again or adding a coupling inside the wall.

Cold weather and freezing

These are two different questions.

Installing in the cold

An expansion joint works because the tube shrinks back over the fitting. In cold air the tube shrinks back more slowly. Viega, which sells a press system, says the wait before pressure testing can reach 24 hours in low temperatures, and that hot weather causes the opposite problem, with the tube contracting before the fitting is in. SharkBite also lists expansion as needing setting time before a pressure test, while its crimp, press and push-to-connect systems can be tested right away. REHAU says its compression-sleeve expansion system (EVERLOC+) needs no wait for pressure testing, even in cold conditions. That is REHAU’s claim about its own system.

Water freezing inside the pipe

The Plastics Pipe Institute’s report TR-52, as summarized by ASPE, says the flexibility of PEX typically lets it expand without cracking when its water freezes, and return to size on thawing. It also says installation problems can still cause failures, and that freezing in any pipe should be prevented. The summary speaks of PEX as a class and does not rank A over B. Uponor, which sells PEX-a, says PEX-a can expand up to three times its diameter and cites TR-52 for PEX-a’s freeze/thaw resiliency. None of the sources I opened shows PEX-B failing where PEX-A survives, so treat any claim that one letter survives freezing better as unproven. Either way, insulate exposed runs and consider a freeze alarm for a place that can get cold.

Pressure and burst strength

Both letters must clear the same ASTM F876 floor. Uponor quotes that floor as a minimum burst pressure of 480 psi for 1/2-inch pipe and 475 psi for 3/4-inch and larger at 73.4°F. Apollo, which sells both types, lists identical ratings for its PEX-A and PEX-B: 200°F at 80 psi, 180°F at 100 psi and 73.4°F at 160 psi, with operating conditions not to exceed 140°F at 80 psi. Uponor gives the same domestic hot water limit of 140°F and 80 psi.

Our arithmetic: 475 psi divided by 80 psi is about 5.9, so the minimum burst pressure is nearly six times the 80 psi operating limit those makers list.

Above that floor, the makers each claim their own product does better. Uponor says its PEX-a tests to nearly double the burst requirement. Viega says its PureFlow PEX-B has a higher bursting pressure than PEX-A. Both are claims about their own lines. I found no source that compares A and B under one test, so I do not rank them on burst.

Chlorine, UV and the print line

Chlorine in hot water is what ages PEX from the inside, which is why ASTM F876 includes an oxidative-stability test in chlorinated water. Both types are tested for it, and both can be rated at the top class. The rating is printed on the tube as a four-digit material designation code, per SharkBite and Viega:

• First digit, chlorine resistance: class 5 is the highest. Viega’s table lists class 5 as 100% at 140°F under ASTM F2023.
• Second digit, UV resistance: class 3 is the highest, six months. Class 1 is one month and class 2 is three months (ASTM F2657, per Viega). Class 0 is not tested or rated.
• Last two digits, pressure rating: 06 on all U.S. PEX, meaning 160 psi at 73°F.

The top code is PEX 5306. SharkBite says both its PEX-a and PEX-b carry it. Viega notes the code shows a product meets a class, not by how much it beats it. The letter does not decide the code. Apollo lists its PEX-B as “PEX 5006”. In Viega’s table a UV digit of 0 means not tested or rated. That is our reading of Apollo’s code, so ask Apollo before relying on it.

For a hot recirculation loop, look for chlorine class 5 on the tube and check the maker’s recirculation limit. Apollo says its PEX can be used in continuously recirculating systems up to 140°F while maintaining chlorine resistance. Do not buy on the letter alone. Zurn and Viega (both PEX-B) claim the highest chlorine ratings, and Uponor says its PEX-a meets the highest requirement, so the letter does not settle it.

Sunlight

UV windows are per product. Uponor says white AquaPEX has one month of UV resistance and red and blue AquaPEX six months. Zurn lists up to six months. REHAU says its RAUPEX UV shield pipe has up to one year. These are construction and storage windows, printed on the tube. They are not permission to leave PEX in the sun.

Warranties

Every maker I read lists 25 years: Uponor on AquaPEX pipe and ProPEX fittings (transferable, limited), Zurn on its PEX products, Viega on PureFlow “when installed as a system,” SharkBite as a 25-year system warranty, and REHAU on RAUPEX pipe (limited). Zurn says its warranty also covers reasonable repair costs such as drywall and painting after a product leak or failure. Viega and SharkBite tie coverage to their own system parts, and Uponor’s covers its pipe and ProPEX fittings together, so a job that mixes brands of tube, fitting and tool may not be covered. Read the warranty for the exact combination before you buy, and ask a contractor to name the system in writing.

Radiant floor heating: check for an oxygen barrier

For radiant floor heating and other closed-loop hydronic systems, the question is not A or B. It is whether the tube has an oxygen barrier. SharkBite explains that the barrier limits oxygen passing through the pipe wall, which prevents corrosion of ferrous metal parts in the heating system (SharkBite oxygen barrier PEX). Uponor lists its standard AquaPEX tube as suitable for hydronic heating where the system has no ferrous corrodible components, or where those parts are isolated from the pipe (Uponor PEX pipe).

Barrier tube is not automatically drinking-water tube, either. Uponor’s Wirsbo hePEX has an oxygen barrier to DIN 4726 for radiant heating and is also listed to NSF 61 for potable water (Uponor Wirsbo hePEX); SharkBite’s oxygen barrier PEX is approved for non-potable radiant heating systems. Before one coil does both jobs, check that the maker lists it for both: an oxygen barrier and potable water.

What is true of both

• Keep it out of sunlight. See the UV windows above. Stored coils belong in their packaging.
• Mind the water heater connection. Uponor says domestic hot water operation should not exceed 140°F and 80 psi. Codes and water heater manuals differ on how PEX connects at the tank, so check yours.
• Support it properly. Uponor lists 32-inch horizontal support spacing for bare PEX 1 inch and smaller, 48 inches for 1 1/4 inch and larger, and 5 feet vertically, and notes that some codes require 32 inches for all sizes. Other makers list their own spacing.
• Burying it. Uponor says its PEX pipe and its engineered-polymer ProPEX fittings are approved for direct burial, and that brass fittings need at least a 6-mil poly wrap. SharkBite says poly fittings are burial-approved and brass must be wrapped. Check the exact product.
• Mixing letters is allowed with care. Viega says different PEX types can share an installation if every connection uses fittings and tools approved for that specific tube. Expansion fittings are the one to double-check.

So which should you use?

Still deciding between PEX and something else? We put all three side by side in PEX vs copper vs CPVC. If the appeal of PEX is avoiding a torch, press vs soldering is worth reading. For a whole-house job, our repipe cost breakdown covers the labor side. Running a home run to each fixture? Our PEX manifold guide sorts manifolds by port connection: crimp or clamp, expansion, or push-fit.

The gear for each system

Heads up: the product links below are Amazon affiliate links. You pay no more, and as an Amazon Associate we earn from qualifying purchases.

• SharkBite 1/2-inch blue PEX-B coil (U860B100): SharkBite says its PEX-b is code 5306 and works with its crimp, press and push-to-connect systems.
• SharkBite 1/2-inch blue PEX-A coil (UA60B100): the PEX-A version of the same coil. The listing says it works with expansion (F1960), push-to-connect, and plastic and brass crimp fittings.
• DeWalt 20V MAX PEX expander kit (DCE400D2) (not linked: third-party seller only on 10/3/2026): the listing says it expands 3/8 to 1-inch PEX Type-A tubing, uses DeWalt PEX heads and is compatible with Milwaukee and Uponor heads. Sold by a third-party seller.

More options: our PEX starter kit guide and crimp & cinch tool guide.

Frequently asked questions

Is PEX-A better than PEX-B?

Not as a rule. Both are built to ASTM F876 and sold for drinking water, and Viega and SharkBite both say the letter names a manufacturing method, not a quality grade. Uponor says PEX-a has the edge on kink repair and tight bends, and it is the pipe made for expansion fittings. SharkBite says PEX-b is offered in more sizes and works with crimp, press and push-to-connect fittings. Pick by the fitting system, the tools you own and the size of the job.

What is the difference between PEX-A and PEX-B?

The manufacturing method. PEX-A is made by the peroxide (Engel) method and PEX-B by the silane (moisture-cure) method. Both are copper tube size and both are built to ASTM F876. In practice the difference shows up in fittings and kinks. PEX-A is the pipe for cold-expansion fittings, and Uponor says only PEX-a can have a kink heated out. PEX-B is joined with crimp, clamp, press or push-to-connect fittings.

Can you use PEX-B fittings on PEX-A tubing?

Fittings are not sold by letter, but fitting systems do differ by tube. “PEX-B fittings” usually means insert fittings with a crimp or clamp ring. SharkBite says its crimp and clamp system connects any type of PEX, so those work on PEX-A too when the tube maker lists them. Expansion is the one that does not carry over the other way: SharkBite lists its expansion fittings for PEX-a or PE-RT only. Read the print line on the tube for the fitting standards it is approved for.

Are PEX-A and PEX-B fittings the same?

Not all of them. The pipe sizes match, because PEX-A, -B and -C are all copper tube size under ASTM F876. The fitting systems differ. SharkBite sells expansion fittings for PEX-a or PE-RT only, and crimp, clamp, press and push-to-connect fittings for either type. Zurn goes the other way: it says its PEX-B is certified for both F1807 crimp fittings and F1960 expansion fittings. The fitting maker’s list for your exact tube decides.

Does PEX-B restrict water flow?

Insert fittings sit inside the tube, so each joint narrows the bore a little. SharkBite says an expansion fitting’s internal diameter is closer to the pipe’s, which can help keep flow up. On a short run it rarely matters. On a long run with many elbows and tees, expansion fittings or a larger trunk line are the fixes I would look at. That last part is my own rule of thumb, not a maker rating.

Which PEX has better chlorine resistance?

Neither letter wins on its own. Chlorine resistance is a class printed on the tube, and the top class is 5. SharkBite says both its PEX-a and PEX-b are code 5306, and Viega, Zurn and Uponor each say their own tube meets the highest chlorine rating. Read the print line, especially for a hot recirculation loop, and check the maker’s recirculation limit.

Can PEX be exposed to sunlight?

Only for the window the tube is rated for. Uponor says its white AquaPEX has a one-month UV resistance and its red and blue AquaPEX six months. The top UV class on the print line is 3, which is six months. Those windows are for construction and storage. Keep coils in their packaging, and never leave PEX exposed outdoors long term.

Can you fix a kink in PEX-B?

Cut the kink out and join the ends with a coupling. Uponor says heat repair works only on PEX-a. Viega says heat repair is possible on some products but is slow, and the tube is more likely to kink again in the same spot, so it recommends cutting the kink out and using a fitting.

Is PEX-A or PEX-B better in freezing weather?

The sources I opened do not name a winner. The Plastics Pipe Institute says PEX in general typically expands when its water freezes and returns to size after thawing, but that installation problems can still cause failures and that freezing should be prevented in any pipe. Uponor says PEX-a can expand up to three times its diameter. Installing in the cold is a separate issue: expansion connections shrink back more slowly, and Viega says the wait before a pressure test can reach 24 hours in low temperatures.

Can you mix PEX-A and PEX-B in the same house?

Yes, if every connection uses fittings and tools approved for that specific tube, according to Viega. SharkBite lists its press, push-to-connect and crimp systems for both types. Do not assume a fitting approved for one tube is approved for another. Follow the manufacturer’s listing.

Sources

Maker and standards pages, read September 29, 2026. The ASTM pages are the free abstracts; the standards themselves are paid and were not opened.

• ASTM F876: Crosslinked Polyethylene (PEX) Tubing (abstract and scope: required tests, UV resistance, degree of crosslinking)
• ASTM F877: PEX Hot- and Cold-Water Distribution Systems
• ASTM F1960: Cold Expansion Fittings with PEX Reinforcing Rings; ASTM F1807: Metal Insert Fittings with Copper Crimp Ring; ASTM F2159: Plastic Insert Fittings with Copper Crimp Ring; ASTM F2098: Stainless Steel Clamps
• ASPE Pipeline on PPI TR-52: PEX freeze-break resistance
• Uponor customer support FAQ: cross-linking levels, kink repair, bend radius, burst floor, UV, freezing, burial, support spacing, warranty
• SharkBite: The Differences Between PEX-A, -B and -C; SharkBite: Which PEX Connection Is Best?
• Viega: PEX-A vs PEX-B vs PEX-C (print-line code table, kink repair, mixing types); Viega: The Truth About Types of PEX; Viega: PEX Press vs Cold Expansion; Viega PureFlow system
• Zurn PEX and Zurn: The Expansion of PEX (PEX-B certified for F1807 and F1960; warranty)
• Apollo PEX-B pipe and Apollo PEX-A pipe (ratings; print code)
• REHAU EVERLOC+ compression-sleeve system (cold-weather claim; UV shield pipe; warranty)
• SharkBite: Oxygen Barrier PEX Pipe (oxygen barrier purpose; non-potable radiant approval)
• Uponor: Wirsbo hePEX (DIN 4726 oxygen barrier; NSF 61 listing)
• Uponor: PEX pipe and rings (AquaPEX hydronic use without a barrier)

For the plumbers reading this

Most of this site is written for homeowners — this page clearly isn’t. If you’re in the trade and want the occasional straight-shooting note when I publish something like this (fittings comparisons, tool guides, code changes), drop your email. No spam, no course funnel, written by a licensed GA journeyman.