COMPARISON
PEX versus multilayer: which is safer in screed
Updated: 2026-08-19
Both are flexible, both come in coils, so they get mixed up constantly. One difference drives everything: multilayer has an aluminium layer, PEX doesn't. PEX is cheaper and tougher on bends; multilayer holds its shape instead of springing back.
Point by point
| Criterion | PEX | Multilayer |
|---|---|---|
| Wall structure | uniform cross-linked polyethylene | polyethylene — aluminium — polyethylene |
| Holds a bend | no, it springs back | yes, bend by hand and it stays |
| Oxygen barrier | for heating it needs an EVOH layer — the pipe is marked “PE-Xa/EVOH” or “PE-Xb/EVOH”; not needed for water | the aluminium is the barrier |
| Fittings | axial (sleeve) or press; Eurocone at the manifold | press or compression |
| Price per metre | cheaper | dearer |
| Thermal expansion | noticeable — leave slack in screed | almost none |
| Shape memory | a kink in PE-Xa straightens out with a heat gun; a kink in PE-Xb/c can't be fixed — cut it out | kinked means cut it out |
| Weak spot | kinks on a tight radius, degrades in UV | a kink breaks the aluminium; cuts must be calibrated |
Pipe materialsAll six materials side by side: joining, temperature, price, where each belongs.
Pipe diametersSize ranges of every system, outer vs inner diameter, which pipe pairs with which thread.
Choose PEX when
- Underfloor heating and manifold runs: long circuits in one piece, with no joints in the screed.
- You want axial fittings — a joint that doesn't fear being buried, because the sleeve crimps the pipe with its own material.
- Budget matters and the metreage is long: the price gap adds up over hundreds of metres.
Choose multilayer when
- The run is visible: the pipe keeps the bend you gave it instead of springing off the wall.
- Connections to radiators and fixtures where you want a neat angle without a fitting.
- You have no press tool and the joint will stay accessible: a compression fitting goes together with an ordinary spanner.
Myths
“PEX isn't for screed — it's just plastic.”
Screed is exactly what it's made for: one continuous circuit with no joints beats any pipe that has connections buried in a floor.
“Multilayer bends any way you like, there's aluminium in it.”
A tight radius cracks the aluminium layer and it starts working against you. Minimum radius by hand is 5 diameters (80 mm for 16 mm pipe); with a bending spring or a pipe bender, 3 diameters.
“The only difference is price.”
The difference is shape memory. That decides whether a visible run looks straight and how obedient a floor circuit is while you lay it.
Common questions
What is the difference between PEX and multilayer?
Multilayer has a layer of aluminium between two layers of polyethylene; PEX does not. That is why multilayer bends by hand and stays put while PEX springs back — and why PEX is cheaper and survives bending better.
Which one goes into an underfloor heating loop?
Both work, but PEX is cheaper over long loops and its axial fittings are considered the safest to pour into screed. What matters more is running each loop in one piece, with no joint inside the floor.
Do I need an oxygen barrier?
For heating, yes: buy PEX with an EVOH layer, otherwise oxygen passes through the wall and the cast iron, steel and pump start to rust. Multilayer needs no separate barrier — the aluminium does that job.
Related pages
Check it in the builder, not at the store
Lay your assembly out in easy-pipe — parts only connect when diameter and thread genuinely match.