Confirm the right topic before starting work: multilayer pipe or multilayer insulation?
What “multilayer pipe” means in 2026 (PER-AL-PER, heating and sanitary applications)
In renovation, “multilayer pipe” almost always means a PER aluminium PER pipe, often written PER-AL-PER. It is used for heating circuits (radiator flow and return, underfloor heating subject to the manufacturer’s requirements) and for plumbing/sanitary use (cold water / hot water), installed with press fittings or compression fittings, dedicated jaw profiles and brand compatibilities to be locked down in the quotation.
Signs that point to a multilayer insulating composite (to avoid going off topic)
If the request mentions a “roll”, “stapling”, “air gaps” or a “reflector”, you are more likely dealing with a multilayer insulating composite, sometimes called thin insulation. In that case, the issue is not the sealing of a joint but proving performance (declared thermal resistance, technical approval, installation conditions). Your multilayer expertise is mainly there to avoid mixing products and rules.
Check landing pages and manufacturer documents before writing or pricing
Before any technical note or costing, cross-check the landing page with the exact reference, the technical datasheet, the certificate (NF, CSTBat or equivalent) and, where applicable, the technical approval. Keep these manufacturer documents in the site file. That is what secures the choice of fittings, tooling and installation requirements.
Preparing the pipes: the steps that prevent 80% of leaks
Square cut with the right pipe cutter: why a saw is risky
On multilayer pipe, a cut that is not square is enough to put the O-ring under stress. A dedicated pipe cutter limits ovalisation and leaves a clean edge. With a saw, you often end up with aluminium swarf, burrs and micro-tears in the inner layer. The result is either a poor fit of the fitting or a sheared seal during assembly.
Calibration and chamfering are mandatory before inserting the fitting
After cutting, calibrate to restore the correct diameter, then chamfer. The chamfer guides insertion and prevents the seal from rolling. Use the tool specified for the fitting system, not a file. An uncalibrated pipe can stop too early and you end up forcing it to an incorrect insertion depth.
Cleanliness, ovalisation and insertion depth: your immediate checks
Before crimping, wipe the end clean and visually check the seal and the stop. Mark the insertion depth with a marker, push in fully to the stop, then check the mark after pressing. This discipline makes all the difference on site, and it is part of a multilayer expertise based on inspection, not on talk.
Connections and crimping: your multilayer expertise at the critical point
Seal and stop: check presence, condition and position before assembly
On multilayer pipe, the leak rarely comes from the pipe. It comes from the fitting. Your expertise in multilayer systems is exercised by checking the seal and the stop before insertion. After a square cut and calibration, make sure the seal is present, clean, not twisted and seated in its groove. Confirm the stop and the insertion depth. Mark the depth with a marker, then insert up to the mark.
Choosing the right jaw and the right crimp profile: avoid the “if it fits, it’s fine” mistake
A similar-looking profile may go into the fitting and produce an invisible non-conformity. Work with the tube-fitting pair from the same system. Validate the diameter, jaw profile and die condition. Reject undocumented brand mixing. On the tool, note the last maintenance date and the jaw reference.
Visual inspection of the crimp and traceability: what you must verify on site
After crimping, check the impression and alignment. The zone should be even, with no offset. Check for pipe presence in the inspection window where one exists. Before closing up, document it with a simple record and a pressure test before burying.
- Photo of the crimped fitting and insertion mark.
- Diameter, profile, jaw reference.
- Date, operator, pressure test before burying.
Installation and constraints: bending, expansion, protection and compatibility
Minimum bend radii: with or without a spring, what you must respect
With multilayer pipe, your reference remains the manufacturer’s minimum bend radius. Without a tool, the risk is ovalisation and microcracking of the aluminium layer. When bending, work on calibrated pipe, use a spring or a bending tool, and reject any “hot” bending. Your multilayer expertise also shows in inspection. No kink, no flat spot, and free passage through the gauge before crimping.
Expansion: less than PEX, but real (and how to handle it in 2026)
Expansion is significantly restrained by the aluminium layer, but it still exists on long heating and DHW runs. Install fixed points, sliding clips where the pipe needs to move, and allow for extra length at direction changes. In 2026, record your choices on the installation drawing and calculation note. That is what holds up if something goes wrong.
Concealed runs, sleeves and tube/fitting compatibility: liability issues
For concealed sections, always protect the pipe with a continuous sleeve. No hidden fitting outside an accessible area. As for materials, do not mix pipe and fittings on a hunch. Require documented compatibility (jaw profile, tolerances, technical approval). Keep the references and batch numbers. That is your evidence if the loss comes from an unvalidated assembly.
Leak control: pressure testing and checks before closing
Pressure testing: when to do it, on what, and how
Carry out the test before closure, once all fittings are crimped and all components are installed. Isolate the circuit, pressurise it with a test pump and a calibrated pressure gauge, then allow a stabilisation phase. Then maintain the test pressure required by the applicable standard and the manufacturer. Any measurable drop calls for leak location and repair, not a “tighten it a bit”.
Sensitive points to inspect: fittings, bends, penetrations and repairs
Your multilayer expertise lies in the details. Visually check the full seating against the stop, the presence of the seal, pipe cleanliness (calibration, chamfer) and tube-fitting compatibility. At bends, check for ovalisation and compliance with the minimum radius. At penetrations, require a continuous sleeve and clips that allow expansion to work.
Closing linings and refilling: your final anti-loss checklist
Before closing, check
- Insertion-depth marks visible on every crimped pipe
- No stress on the fittings (pipe aligned, no torsion)
- Sleeving protections at concealed passages and penetrations
- Traceability. Dated photos and recorded test pressure in the report
