PEX-AL-PEX vs. other pipe types: comparison with copper, plastic and PEX-B

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PEX-AL-PEX vs. other pipe types: comprehensive comparison with copper, plastic and PEX-B

When deciding which pipe to use for heating, underfloor heating or drinking water distribution, you're facing a choice that will affect the performance of the entire installation for decades to come. There are several types of pipes on the market – copper, conventional plastic (PP, PE), PEX-B and PEX-AL-PEX – and each has its supporters and detractors. The problem is that most comparisons you find online are either too superficial or written by sellers with an interest in promoting a specific product.

In this article, we'll look at things without embellishment: what each pipe can really do, where it falls short, and for which situations each solution is truly the most suitable. This is based on experience from everyday installation practice – from dozens of projects, from family houses through bathroom core renovations to production halls.

What exactly is PEX-AL-PEX and why does it have three layers

Before we start comparing, we need to know what we're comparing with. PEX-AL-PEX is a composite pipe made of three layers: an inner layer of cross-linked polyethylene (PEX), a middle layer of aluminum (Al) welded butt-to-butt or overlapped, and an outer protective layer, again of PEX. These three layers are bonded together with a special adhesive to form one monolithic whole.

The aluminum layer is not just filler – it performs several functions at once. First, it ensures shape memory: the pipe holds the desired shape after bending without springing back, which is a huge practical advantage during installation. Second, it acts as an oxygen barrier, preventing oxygen from diffusing through the pipe wall into the heating water. And third, aluminum increases the strength of the whole tube, allowing a thinner wall to be used while maintaining good pressure parameters.

The outer diameter typically ranges from 16 mm to 63 mm; for heating and underfloor heating distribution, the most common dimensions are 16×2 mm, 20×2 mm and 26×3 mm. For example, PEX-AL-PEX 16×2 pipe is the standard for underfloor heating loops, PEX-AL-PEX 20×2 pipe is used as a distribution line from the manifold, and PEX-AL-PEX 26×3 pipe covers the connection to the heat source or distribution risers.

Copper: the golden standard with real limitations

Copper piping is deeply rooted in installation tradition – and not without reason. Copper has excellent mechanical strength, withstands temperatures very well (working temperature up to 110 °C, briefly even more), is biologically safe for drinking water, and with proper installation lasts 50 years without problems. Soldering copper is a craft that every experienced installer masters perfectly.

Nevertheless, copper has several real disadvantages in today's practice that push it out of many applications:

Price: Copper is a commodity traded on exchanges and its price has risen significantly in recent years. DN15 (3/4") copper pipe typically costs 3–5x more than comparable PEX-AL-PEX at the same inner diameter.
Corrosion with aggressive water: Soft water with low pH (below 7.0) and a high content of free CO₂ can corrode copper, even from the inside. In areas with acidic water, we have seen copper piping fail within 10 years.
Electrochemical corrosion when mixing materials: Copper is a noble metal and together with aluminum bodies (radiators, circulation pumps) creates a galvanic cell. The result is premature corrosion of the aluminum – and here's the irony: in systems with aluminum radiators, copper is problematic.
Thermal expansion: Copper expands less when heated than plastic (about 0.017 mm/m/°C), but for long runs, expansion must be accounted for and compensators installed.
Labor-intensive installation: Soldering requires an open flame, cleaning of joints, flux and tin – this complicates work in insulated structures or near flammable materials. Moreover, each joint requires time and skill.
Rigidity: Copper can be bent, but without a special bending tool it easily kinks. More fittings are needed for more complex routing.

In practice, copper remains an ideal choice where maximum mechanical resistance is needed when exposed to UV radiation or mechanical damage (e.g. outdoor lines), when connecting to a boiler in a boiler room, or where the customer explicitly insists on a traditional solution. For underfloor heating or long runs in timber-frame buildings, most experienced technicians no longer recommend it.

Polypropylene (PP) and polyethylene (PE): cheap, but with serious compromises

Conventional plastic pipes made of polypropylene represent the best-selling group of pipes for cold and hot water distribution in residential construction. The reason is simple: they are cheap, easily available, and their installation (heat welding) doesn't require special tools costing thousands of euros. A welded joint is permanent and requires no sealing elements.

Where PP pipes fall significantly short:

Thermal expansion: PP has a linear thermal expansion coefficient of about 0.07–0.08 mm/m/°C, which at 60 °C over a 10 m run results in an expansion of 42 mm. This is a huge figure that the installation must accommodate with expansion loops or movable fixings. In floors, PP is practically unusable without special measures.
Oxygen diffusion: Standard PP pipe doesn't let oxygen through the wall – that's an advantage. But water with aggressive chemistry can stress it in other ways.
Rigidity vs. brittleness: PP is relatively rigid at normal temperatures, but becomes brittle below 0 °C and cracks easily. In unheated spaces, this is a serious risk.
Pipe diameter: Thick walls of PP pipes (SDR 11 for hot water) actually reduce the inner diameter. At a 20 mm outer diameter, the inner diameter is only 13.2 mm – compared to the equivalent PEX-AL-PEX 20×2 (inner diameter 16 mm), this is a sensitive difference for hydraulics.
Installation in walls: PP joints are large and fittings bulky – in spaces with plasterboard or masonry, they are less suitable than thin composite pipe joints.

PP pipe makes sense for cold water lines in exposed plant rooms, in basements where expansion is not an issue, or for distribution where discreet installation is not required. For underfloor heating, it is practically excluded.

PEX-B: flexibility yes, but without shape memory and with the oxygen question

PEX-B (cross-linked polyethylene produced by the silane method – the so-called Engel or Silane process) is a purely plastic pipe without an aluminum layer. It is extremely flexible, easy to bend, resistant to freezing (unlike PP), and cheaper to manufacture than PEX-AL-PEX.

Why, despite this, many technicians prefer it only for specific applications:

No shape memory: PEX-B returns to its original shape after bending – the so-called "plasticity memory". When laying underfloor loops, this means the pipe wants to spring back straight and must be fixed every 30–50 cm. PEX-AL-PEX holds its shape after bending – laying is faster and more convenient.
Oxygen diffusion: Without an aluminum layer, oxygen diffuses through the pipe wall into the water. In a closed heating system, this leads to oxidation of metal components (boiler, pump, radiators, valves). There is a PEX-B version with an EVOH barrier, but it is far less effective than aluminum.
Thermal expansion: PEX-B expands similarly to PP – about 0.06 mm/m/°C. For hot distribution lines, expansion must be addressed. Thanks to aluminum, PEX-AL-PEX has an expansion of only 0.025 mm/m/°C – 60% lower.
Pressure parameters: Pure PEX-B without aluminum has lower maximum operating pressures at the same wall thickness than PEX-AL-PEX. For heating systems with pressure above 6 bar, this is a relevant limitation.
Joints: Crimping PEX-B requires special fittings (a different system than for PEX-AL-PEX) and joint quality depends on the precision of the crimping tool – under-crimping is harder to detect visually than with composite pipe.

PEX-B is an excellent pipe for sanitary cold and hot water distribution in walls, where flexibility is important and it's not a closed heating loop. For underfloor heating, most installers are now gradually replacing it with PEX-AL-PEX precisely because of the oxygen barrier and shape memory.

Detailed comparison of PEX-AL-PEX with all types – parameter table

Parameter	Copper	PP plastic	PEX-B	PEX-AL-PEX
Shape memory (bending)	✅ yes	❌ no	❌ no	✅ yes
Oxygen barrier	✅ yes	✅ yes	⚠️ partial (EVOH)	✅ yes (Al)
Thermal expansion (mm/m/°C)	0.017	0.07–0.08	0.06	0.025
Max. working temperature (°C)	110	70–95	70–80	95 (briefly 110)
Max. working pressure (bar)	10–25	6–10	6–8	10–16
Freeze resistance	⚠️ cracks	❌ brittle	✅ resistant	✅ resistant
Relative price (1 = cheap)	4–5	1	1.5–2	2–3
Joining method	soldering, crimping	welding	crimping, push-fit joints	crimping, screw-fit
Suitability for underfloor heating	⚠️ limited	❌ no	⚠️ conditional	✅ ideal
Lifespan with proper installation	40–50 years	30–40 years	25–50 years	50+ years

Where PEX-AL-PEX truly excels – specific real-world scenarios

Scenario 1: Underfloor heating in a new family house

This is by far the most common application of PEX-AL-PEX today. The customer plans a concrete screed with underfloor heating on the ground floor and upstairs, with a heat pump as the heat source. Why is PEX-AL-PEX the clear choice here? The pipe bends easily, holds its loop shape without fixing, the aluminum barrier protects the heat pump from oxygen-induced corrosion, and the expansion of 1.25 mm/m at ΔT=50°C is low enough not to need special expansion measures in a standard screed.

For this scenario, PEX-AL-PEX 16×2 pipe with loop spacing of 15–20 cm is typical. The distribution line to the manifold is then 20×2 or 26×3 mm. You can read more about loop sizing in the article PEX-AL-PEX pipe for underfloor heating: spacing, loop length and maximum temperature.

Scenario 2: Bathroom core renovation – distribution behind plasterboard

When renovating a bathroom core, the goal is for the distribution to take up as little space as possible in the shafts and pre-walls. Here, copper with its large fittings and need for an open flame loses out. PEX-AL-PEX 16×2 or 20×2 is laid in channels or directly behind plasterboard, fittings are compact, and joining with crimping pliers is fast. The same pipe serves as both the hot water line and the radiator supply – two problems, one solution.

Scenario 3: Boiler room with a gas boiler – radiator distribution

For the main lines from the boiler to the floor manifolds, PEX-AL-PEX 32×3 pipe is now commonly used. System pressure is 2–3 bar, temperature 55–70 °C – PEX-AL-PEX handles this with plenty of margin. Compared to copper, material savings here reach 40–50%, and installation is faster. The only area where copper remains justified in the boiler room is the immediate connection to the boiler in places with temperatures above 95 °C.

Scenario 4: All-timber frame construction

In timber-frame buildings, combining an open flame (copper soldering) with a wooden structure is unacceptable from a fire safety standpoint. PP welding is somewhat safer, but bulky fittings and large expansion are problematic in wooden grooves. PEX-AL-PEX is the clear favorite here: fast crimping, low expansion, flexibility in routing. In addition, VERME pipe, such as VERME PE-AL-PEX 16×2 pipe, offers an even slightly stronger outer layer with a protective sheath suitable for timber-frame construction.

Joints and fittings: where the difference matters in practice

An important part of the comparison is not just the pipe itself, but also the joining system. For PEX-AL-PEX, there are essentially two types of joints: crimped (for permanent and inspectable joints) and screw/compression (for serviceable joints that need access). Both types are combined in practice.

Crimping PEX-AL-PEX requires a calibrator (to prepare the pipe end), a crimp ring, and crimping pliers or a machine. The joint is permanently non-detachable once crimped and requires no internal seals – sealing is ensured by direct contact between the PEX and the fitting. This is an advantage over PP (where the joint is fully bonded, but you can't see inside) and over copper (where poorly applied flux or too little solder can produce a joint that looks good but is actually porous).

With screw fittings for PEX-AL-PEX, the pipe is slid onto the fitting's inner body, and the outer nut is tightened over a seal. The joint is accessible for inspection and, if needed, detachable – useful, for example, when connecting to fittings, a tank, or a manifold. More details on the correct procedure can be found in the article Installing PEX-AL-PEX pipe: bending, crimping and correct joints step by step.

For copper, soft soldering is a proven method, but hard soldering (with silver solder) is banned or restricted at many workplaces. Crimping copper is faster, but fittings are more expensive than for PEX-AL-PEX. PP welding produces a very strong joint, but once set, no adjustment is possible – a mistake means cutting it out and making a new joint.

Hydraulics and flow resistance: something often overlooked

When comparing pipes, material properties are usually discussed, but hydraulics are equally important, and choosing the wrong diameter can mean the system never reaches its calculated output.

The roughness of the inner wall directly affects pressure losses. Measured equivalent roughness values:

Copper: 0.0015 mm (very smooth)
PEX-AL-PEX: 0.007 mm (practically smooth, negligible difference from copper at normal flow rates)
PP: 0.007 mm (similar to PEX-AL-PEX)
PEX-B: 0.007 mm

In practice, this means that at the same inner diameters, the pressure losses between copper and PEX-AL-PEX are minimal – measurable, but insignificant. The real difference occurs in wall thickness: PP pipe SDR11 has a proportionally thicker wall, meaning a smaller inner diameter at the same outer diameter. For example, at an outer diameter of 20 mm: PP PN20 has an inner diameter of 13.6 mm, while PEX-AL-PEX 20×2 has an inner diameter of 16 mm. The difference in flow at the same pressure drop is nearly 40%.

This has a practical impact: when designing PP distribution, you have to go one diameter size up, which increases material costs and reduces PP's price advantage over PEX-AL-PEX. Read more about choosing the correct diameter in the article How to choose PEX-AL-PEX pipe: diameter, wall thickness and pressure parameters.

Lifespan and warranties: what the standards say and what practice shows

Manufacturers of PEX-AL-PEX commonly declare a lifespan of 50 years when operating parameters are respected – temperature up to 95 °C, pressure up to 10 bar. These values are backed by tests according to ISO 15875 and EN ISO 21003 standards. Copper has a similarly declared lifespan, but actual duration strongly depends on the chemical composition of the water.

In practice, we have seen PEX-AL-PEX installations 20–25 years old (from when this material started spreading) with no signs of degradation, corrosion, or pressure loss. On the other hand, copper distribution in areas with softened water or water with low pH shows pinhole corrosion already after 8–15 years.

Important note: the lifespan of PEX-AL-PEX directly depends on the quality of the adhesive layer between PEX and Al. In cheaper, unbranded products, this layer can degrade, causing the layers to delaminate and leaks to occur. It therefore makes sense to choose proven certified products, where the bonding quality is controlled.

Ecological and recycling aspects

Copper is fully recyclable and has high scrap value – which is also why it gets stolen. PP and PEX-B are recyclable as plastic waste, but reusing them is not trivial. PEX-AL-PEX is a composite material made of three different layers, and its recycling is more complex – the aluminum and plastic must be separated. Special recycling lines exist, but they are not yet standard in Slovakia.

On the other hand, the energy intensity of copper production is several times higher than that of PEX-AL-PEX production. And since PEX-AL-PEX retains its shape and requires fewer fittings, the total material consumption for installation is lower. For most customers, ecology is not a deciding factor, but it's good to know.

Frequently Asked Questions (FAQ)

Can I connect PEX-AL-PEX directly to copper pipe?

Yes, direct connection of PEX-AL-PEX to copper pipe is common and technically trouble-free when proper transition fittings are used. The aluminum layer in PEX-AL-PEX is not in direct contact with the water or with the copper, so galvanic corrosion is not a risk in such a joint. A problem would only arise if aluminum and copper came into direct contact in an electrolytic (mineral) water environment – which doesn't happen in a normal closed system. However, it is recommended to use a dielectric fitting when connecting in systems with extensive networks of both materials.

Why isn't PP pipe suitable for underfloor heating?

The main reason is the extreme thermal expansion of PP – at a temperature of 45 °C and a loop 80 m long (which at a 15 cm spacing covers an area of about 50 m²), the pipe expansion when heating from 15 to 45 °C can be up to 140 mm. This expansion in an embedded loop causes internal mechanical stress in the screed, leading to cracking. PEX-AL-PEX has an expansion of only about 55 mm under the same conditions, which is much less risky. Moreover, 16 mm PP pipe is bulky, hard to bend into small radii, and doesn't hold the loop shape without fixing every 20 cm – which is very impractical when laying it.

Is PEX-AL-PEX also suitable for drinking water distribution?

Yes, PEX-AL-PEX approved for contact with drinking water meets hygiene requirements (certification according to Decree 247/2017 Z.z. for materials in contact with drinking water). The inner PEX layer is inert and releases no harmful substances into the water. The aluminum layer is not in contact with the water, so no hygienic risks arise from this either. However, it's important to buy pipe with valid drinking water certification – not every product on the market has it, even if it's sold for drinking water use.

How much does PEX-AL-PEX installation cost compared to copper – total costs?

The material itself for PEX-AL-PEX is 40–60% cheaper than copper at a comparable inner diameter. Labor costs for PEX-AL-PEX are typically 20–30% lower, because crimping is faster than soldering and the pipe is easier to route. Fittings are cheaper for PEX-AL-PEX than for copper, but more expensive than for PP. Overall, PEX-AL-PEX installation comes out 30–50% cheaper than copper, depending on project complexity and regional labor prices. Compared to PP, PEX-AL-PEX is more expensive in materials, but when correctly calculating inner diameters and labor savings, the difference is smaller than it seems.

What is the difference between PEX-AL-PEX and PE-AL-PEX?

Essentially, it's the same thing, just a different designation. PEX means cross-linked polyethylene, while PE without the X is non-cross-linked polyethylene. In piping systems, both abbreviations today refer to cross-linked material – manufacturers like VERME, for example, label their product PE-AL-PEX, while it is in fact the same three-layer composite pipe with the same properties as PEX-AL-PEX. What matters is checking the standard (EN ISO 21003, ISO 15875) and the data sheet content, not just the abbreviation in the name.

Can UV radiation damage PEX-AL-PEX in outdoor installations?

Yes, UV radiation gradually degrades PEX (the outer layer). For short-term outdoor storage (during construction, a few weeks), this is not a problem, but for permanent outdoor installation, the pipe must be protected – either with a UV-stable insulating jacket or routed in a protective conduit. Copper is more resistant in this regard. For permanently exposed outdoor distribution, either copper or PEX-AL-PEX in a protective sleeve is therefore the more appropriate choice.

Conclusion: When to choose PEX-AL-PEX and when to reach for an alternative

After this comparison, it's clear that PEX-AL-PEX is not just a "cheap copper substitute" – it is a distinct material with its own strengths that outperforms traditional solutions in many applications. Its combination of shape memory, oxygen barrier, low thermal expansion, long lifespan and reasonable price makes it the first choice for:

underfloor heating in all types of buildings
heating water distribution in apartment and family houses
installations in timber-frame and low-energy buildings
hot and cold drinking water distribution in indoor spaces
renovations requiring discreet routing behind pre-walls

Copper remains justified in boiler rooms for direct connection to the boiler, in unprotected outdoor distribution, and where the customer insists on a metal solution for principled reasons. PP plastic makes sense for cold water distribution in exposed boiler room and plant room runs. PEX-B finds its place in sanitary cold water distribution in walls, where an oxygen barrier is not critical.

If you want to get a deeper understanding of PEX-AL-PEX, we recommend other articles in our Knowledge Center: What diameter of PEX-AL-PEX pipe do I need for underfloor heating, radiators or water distribution, Minimum bending radius of PEX-AL-PEX pipe and correct shaping technique without kinking, and Common mistakes when installing PEX-AL-PEX pipe and how to avoid them. You can find the complete range directly in the category pipe

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