PEX vs Copper vs Multilayer Pipes: What to Choose for a Renovation

What’s behind your walls matters more than you think

When people plan a bathroom renovation, they think about tiles, taps, shower trays and vanity units. Fair enough. It’s what you see, what you touch, what makes the bathroom look good. But underneath all that are kilometres of pipe that will determine whether your bathroom is still working well in 20 years or starts giving you problems.

Pipes are the invisible infrastructure of the bathroom. And like everything invisible, they’re ignored until they fail. A leak behind a tile can ruin a €10,000 renovation in an afternoon. We’ve seen it. More than once, in apartments in Valencia where the previous renovation used cheap or incompatible materials.

Today there are three main options for bathroom plumbing: PEX (cross-linked polyethylene), copper and multilayer (PEX-AL-PEX). Each has its advantages, drawbacks and ideal context. Let’s compare them with data, not anecdotes.

PEX: the cross-linked polyethylene that has conquered plumbing

What PEX is

PEX stands for “cross-linked polyethylene.” It’s a plastic tube whose molecules are interlinked (cross-linked) to give it pressure and temperature resistance. It’s manufactured in three variants according to the cross-linking method:

• PEX-A (Engel/peroxide method): Cross-linking during extrusion. Result: more flexible tube with “shape memory” (can be expanded and returns to its diameter). Uniform cross-linking of 70-80%.
• PEX-B (silane/moisture method): Cross-linking after extrusion. Result: slightly more rigid tube than PEX-A, cheaper to manufacture. Cross-linking of 65-70%.
• PEX-C (electronic/radiation method): Cross-linking by electron bombardment. Result: less uniform cross-linking (more on the surface, less at the centre). Less widespread.

In Spain, PEX-A and PEX-B dominate the residential market. Our plumbers primarily work with PEX-A for its superior flexibility.

PEX advantages

• Flexibility: Bends without fittings, reducing connection points (each connection is a potential leak point)
• No corrosion: Doesn’t oxidise, doesn’t build up internal limescale, doesn’t degrade with aggressive water
• Lightweight: A 20 mm PEX tube weighs 0.11 kg/m. The copper equivalent weighs 0.63 kg/m
• Noise absorption: Plastic dampens “water hammer” (that metallic bang when you close a tap quickly)
• Frost resistance: PEX-A can expand up to 3% of its diameter without breaking. If water freezes inside, the tube expands and then returns. Copper cracks
• Quick installation: No soldering, no specialised cutting tools

PEX drawbacks

• Not suitable for outdoor use: UV rays degrade polyethylene. Must always be installed protected (recessed or in conduit)
• Permeability: Can allow oxygen passage (relevant for heating circuits, less so for sanitary plumbing)
• Connections: PEX fittings (especially crimp) require specific tools. If your plumber doesn’t have the crimping tool, they can’t work with PEX
• Thermal expansion: Greater than copper. On long straight runs, expansion allowance is needed

Copper: the time-tested material

What it is (and why it’s still here)

Copper has been used in plumbing for over 5,000 years (literally — the Egyptians already had copper pipes). In Spain, it was the standard material from the 1960s until the early 2000s, when PEX and multilayer started gaining ground.

Why is it still a valid option? Because it’s an extraordinary material: naturally antibacterial (bacteria die on contact with copper within hours), 100% recyclable, with a proven durability of 50-70 years, and a rigidity that allows aesthetically impeccable installations.

Copper advantages

• Extreme durability: 50+ years under normal conditions. There are copper pipes from the 1960s that are still perfect
• Antibacterial: Copper eliminates 99.9% of bacteria on contact within 2 hours (EPA-certified property)
• Fire resistance: Doesn’t melt or emit toxic gases. A1 fire reaction classification
• Rigidity: Doesn’t deform, doesn’t bend over time. Copper installations maintain their shape for decades
• Recyclable: 100% recyclable without loss of properties. Recycled copper is identical to virgin
• Total oxygen barrier: Complete impermeability. Crucial for heating circuits

Copper drawbacks

• Price: Copper is traded as a commodity on the stock exchange. In 2027, a 22 mm copper tube costs €8-12/m. Five years ago it cost €5-7/m. The trend is upward
• Corrosion in acidic water: Water with low pH (<6.5) or high chloride content can corrode copper from the inside. In Valencia, mains water has a pH of 7.2-7.8 (neutral-alkaline), so it’s not a common problem. But in areas with acidic well water, be careful
• Slow installation: Tin soldering requires experience, cleanliness and time. Press fittings speed up the process but increase fitting costs
• Water hammer: The rigid tube transmits vibrations from rapid water closure. It sounds like a “clank” inside the wall. Good plumbers install water hammer arrestors, but not all do
• Theft: Yes, seriously. On construction sites, copper pipe theft is a real problem due to its scrap value

Multilayer (PEX-AL-PEX): the best of both worlds

What it is

Multilayer pipe is a three-layer sandwich:

1. Interior: PEX (water contact, chemical resistance)
2. Centre: Welded aluminium (oxygen barrier, rigidity, dimensional stability)
3. Exterior: PEX (mechanical protection)

The result is a tube that combines PEX flexibility with metal stability. It bends and holds its shape (no fittings needed for each elbow), but isn’t as rigid as copper.

Multilayer advantages

• Bendable and stable: Bends with a bending tool and holds shape. Fewer fittings = fewer potential leak points
• Oxygen barrier: The aluminium layer prevents oxygen diffusion. Ideal for mixed circuits (plumbing + heating)
• Low expansion: The aluminium layer reduces thermal expansion to levels close to copper
• Aesthetics: Can be left exposed without looking “provisional”
• Quick connections: Press fittings identical to copper. Same tools, same timings

Multilayer drawbacks

• Limited bending radius: Although it bends, it has a minimum radius (5x the diameter). If you force it, the aluminium layer fractures and watertightness is lost
• No shape memory: Unlike PEX-A, if you deform a multilayer pipe it doesn’t return to its original shape. If it gets crushed, it stays crushed
• Mid-to-high pricing: More expensive than PEX, similar or slightly less than copper
• Fitting compatibility: Each brand has its own press-fit system. They’re not always interchangeable

Technical comparison: the table you need

Characteristic	PEX-A	Copper	Multilayer
Tube price 20 mm (€/m)	€1.50-3.00	€8-12	€3.50-6.00
Elbow fitting price (€)	€2-5	€4-8 (press) / €0.50 (soldered)	€4-7
Lifespan	25-50 years	50-70 years	30-50 years
Max. continuous temp.	70°C (PEX-A: 95°C peak)	250°C	70°C (95°C peak)
Max. pressure	6-10 bar	16-25 bar	10 bar
Thermal conductivity	0.35 W/mK	380 W/mK	0.43 W/mK
Thermal expansion	0.15 mm/m/°C	0.017 mm/m/°C	0.026 mm/m/°C
Weight (20 mm tube)	0.11 kg/m	0.63 kg/m	0.18 kg/m
Noise	Low (absorbs)	High (transmits)	Low-medium
Frost resistance	Excellent	Poor	Good
Oxygen barrier	No (yes with EVOH)	Yes (total)	Yes (aluminium)
Installation time	Fast	Slow (soldering) / Medium (press)	Medium
Tools	Crimper/expander	Blowtorch or press	Press

What the CTE says (Spanish regulations)

The Technical Building Code (CTE), in its Basic Document HS4 (Water Supply), establishes the requirements that pipe materials must meet:

• UNE-EN ISO 15875: Standard for PEX pipes in water installations
• UNE-EN 1057: Standard for copper pipes
• UNE-EN ISO 21003: Standard for multilayer pipes

All three materials comply with current regulations. There’s no legal restriction on using any of them in a bathroom renovation in Spain. The choice is technical and economic, not regulatory.

What the CTE does require:

• Thermal insulation: All hot water pipes and cold water pipes running through unheated zones must be insulated. Minimum thickness per RITE (Building Thermal Installations Regulation) table
• Circuit separation: Hot and cold water pipes must be separated by a minimum of 4 cm, with hot water always on top
• Expansion: Expansion elements must be provided on straight runs longer than 5 metres

When to choose each material: our recommendation

After overseeing more than 300 bathroom renovations, this is what we’ve learned:

Choose PEX-A when…

• Your budget is tight: The material savings are significant. In an average bathroom with 15-20 metres of pipe, the PEX vs copper difference can be €150-200 in tube alone, plus €50-80 in fittings
• The installation is complicated: In old Valencia apartments with hollow brick partition walls, running flexible tubing is infinitely easier than rigid copper tubes
• Area with frost risk: If the bathroom faces a north facade and pipes run through cold zones (garage, air cavity), PEX is more frost-tolerant
• You want quiet pipes: In bathrooms where pipe noise is a problem (old apartment, thin walls), PEX dampens better

Choose copper when…

• You want maximum durability: If you think “this renovation is for life,” copper is the material that ages best
• The installation will be exposed: In an industrial or loft-style bathroom where pipes remain visible, copper has an aesthetic that plastic can’t match
• Integrated heating circuit: If the bathroom has a radiator or underfloor heating connected to a gas boiler, copper with total oxygen barrier is the safest option
• Your trusted plumber only works with copper: An expert copper plumber will do a better job in copper than in PEX if they lack experience with the latter. The tools and skill matter

Choose multilayer when…

• You want a balance: More stable than PEX, easier to install than copper, mid-range pricing
• The installation has both exposed and recessed runs: Multilayer looks good exposed (more so than PEX) and recesses without issue
• You need to reduce fittings: Multilayer holds bent elbows without fittings. In a bathroom with many direction changes, that reduces connection points
• Plumbing + heating: The aluminium barrier makes it suitable for mixed circuits

Real cost of replumbing a bathroom in Valencia

Let’s get to the real numbers. A typical 5 m² bathroom with sink, toilet and shower needs approximately:

• 15-20 metres of pipe (hot water + cold water + distribution)
• 8-12 fittings (elbows, tees, valves, sanitary connections)
• 4-6 hours of plumber labour

Item	PEX-A	Copper (press)	Multilayer
Pipe (18 m)	€27-54	€144-216	€63-108
Fittings (10 pcs)	€20-50	€40-80	€40-70
Insulation	€15-25	€15-25	€15-25
Labour (5h at €35/h)	€175	€210 (6h)	€175
Total plumbing	€237-304	€409-531	€293-378

The difference between PEX and copper for a bathroom is about €150-230. In the context of a bathroom renovation costing €6,000-15,000 (check our calculator for your case), it’s not a difference that should determine the decision. Choose by performance, not by savings.

Where the economic difference does matter is in whole-property renovations (kitchen + 2 bathrooms + heating) with 80-120 metres of pipe. There, PEX vs copper can mean €800-1,200 difference. That’s worth thinking about.

Common mistakes we see in bathroom renovations

Mixing materials without proper transition

You can’t directly connect copper to PEX with a universal hardware-store fitting. Galvanic corrosion occurs (the copper and the fitting metals react with each other). You need specific transition fittings with a dielectric gasket. In our article on technical errors in renovations we go deeper into this.

Not insulating hot water pipes

The CTE requires it. Many plumbers run the hot water pipe uninsulated “because it’s recessed.” Result: heat loss, condensation on the partition wall and, over time, damp. Insulation costs €1-2/m. There’s no justification for skipping it.

PEX exposed to sunlight during construction

If the plumber leaves PEX pipes unprotected for weeks on a site with open windows, UV radiation degrades the material. We’ve seen PEX pipes with micro-cracks from sun exposure during construction. Protect with tape or install at the end.

Insufficient bending radius in multilayer

If you force a tight bend in a multilayer pipe, the inner aluminium layer fractures. From the outside you can’t see it — the outer PEX layer remains intact. But the oxygen barrier is broken and the pipe may fail long-term. Always use a bending tool and respect the manufacturer’s minimum radius (typically 5x the outer diameter).

Frequently asked questions

Can I connect PEX plumbing to my old copper installation?

Yes, with appropriate transition fittings. A copper press fitting is used on one side and a PEX crimp/expansion fitting on the other, with an intermediate dielectric gasket. It’s a standard practice in partial renovations where only the bathroom plumbing is renewed but not the rest of the property.

Does PEX affect the taste of water?

PEX tubes certified under UNE-EN ISO 15875 pass substance migration controls. In the first days after installation, a slight taste may be noticed (like when you open a new plastic bottle), which disappears after a few days of use. Long-term, there’s no taste impact.

How long does a copper pipe last in Valencia?

With Valencia’s mains water (pH 7.2-7.8, average hardness 25-35°f), copper has a 50-70 year lifespan without problems. We’ve removed copper pipes from 1970s apartments in the Eixample that were in perfect internal condition. They’re only changed for insufficient cross-section or layout reconfiguration.

Is multilayer better than PEX?

Not necessarily “better” — it’s different. Multilayer holds shape better, has an integrated oxygen barrier and expands less. PEX-A is more flexible, cheaper and has shape memory. For pure bathroom plumbing, both are excellent. For mixed circuits (plumbing + heating), multilayer has the advantage due to its aluminium barrier.

Should my plumber know how to work with all three materials?

Ideally yes. In practice, many veteran plumbers only work with copper (it’s what they learned) and many young ones only with PEX. A good plumber masters at least two of the three. In Bathscape renovations, our plumbing team works with all three materials and chooses based on the case. See how we work on our how it works page.

What pipe does Bathscape recommend?

Our first choice for bathroom plumbing is PEX-A with expansion connections. It’s the combination that best balances cost, durability, ease of installation and performance. For circuits combining plumbing and heating we use multilayer. And for exposed design installations, copper with a natural finish.

We don’t have “sponsorship” from any manufacturer. We choose what’s best for each project. You can see examples in our completed projects or explore options in the configurator.

Conclusion: the perfect pipe doesn’t exist, but the informed choice does

There’s no universally better material. There are contexts where each one excels. What matters is that your plumber knows all three options, that the choice is based on your home’s conditions (not on what was in the warehouse that morning) and that the installation is done according to regulations.

And above all: that in your renovation budget, plumbing gets the importance it deserves. It’s not the place to cut corners. An ugly tile gets changed in a day. A failing pipe forces you to break the wall, rip out tiles and start again. The cost difference between the cheapest and best plumbing is €200-300 in a bathroom. Spend it. Your future self will thank you.

If you’re planning your renovation, use our calculator for an initial estimate or request a personalised quote. Read the reviews from those who’ve already renovated with us and verify that what’s behind the walls is done as well as what’s visible.