Quick answer: If your LSZH jacket passed IEC 60332 and IEC 61034 but chalked, cracked or lost half its elongation after a year in the sun, the flame retardant package is the reason. At 55–65 % metal hydroxide, the filler surface adsorbs the hindered amine light stabiliser and quietly disarms it. UV performance in LSZH is a filler-treatment problem, not a stabiliser dosage problem.
Almost every LSZH specification we get sent is written around three numbers: IEC 60332 flame propagation, IEC 61034 smoke, IEC 60754 acid gas. Those three are the easy part. Any competent LSZH cable compound passes them.
What the specification usually does not say is where the cable lives. In a riser shaft, indoors, never wet, never in daylight — a standard HFFR grade will outlast the building. In a duct in Riyadh, an aerial drop in Manila, a solar farm trench in Rajasthan, that same grade can be at half its original elongation in eighteen months. The burn tests will still pass. The cable will still fail.
Why LSZH is structurally bad at weathering
A PVC or PE jacket is mostly polymer. An LSZH jacket is not. To get halogen-free flame retardancy from aluminium trihydroxide (ATH) or magnesium hydroxide flame retardant, you need 55–65 % filler by weight in the sheath — some jacket grades run to 68 %. There is no way around it: these fillers work by endothermic decomposition and water release, so the protection is proportional to how much of it you load.
That means the material is more mineral than polymer. Three consequences follow, and every one of them shows up in service rather than in the burn lab.
One: the stabiliser gets eaten. Hindered amine light stabilisers (HALS) are basic, and metal hydroxide surfaces are covered in hydroxyl groups. The HALS adsorbs onto the filler instead of staying available in the polymer phase. This is documented in the cable patent literature — when a large amount of metal hydroxide is present, the light stabiliser is adsorbed by the filler and good weather resistance is simply not obtained. You can double the HALS loading and get very little back, because the filler surface area scales too.
Two: the compound drinks water. Untreated ATH and MDH are hydrophilic. In wet ageing, water absorption drives insulation resistance down and creates the conditions for tracking. This is the real content behind the queries about water-resistant and moisture-barrier LSZH grades — it is a filler-surface question.
Three: you lose the mechanical margin you needed anyway. Typical HFFR sheath compounds land at 140–155 % elongation at break and around 11 MPa tensile. the IEC 60502 ST8 halogen-free sheath designation asks the material to still hold 9 MPa tensile after air-oven ageing. You are not starting with much headroom. A weathering test that costs you half your elongation takes you straight through the floor — whereas a PE jacket starting at 500 % can lose the same fraction and still be fine.
What actually fixes it
Carbon black, correctly specified, does most of the work. Not “black masterbatch” — specified carbon black. The number that matters is primary particle size: 20 nm at 2–2.5 % loading is the well-established recipe for outdoor polyolefins, and ASTM D1248 requires not less than 2 % for Class C weather-resistant material, with 35 nm or finer for the jacketing grades. A 60 nm furnace black at 1 % will make the cable black and do almost nothing for UV.
Then the filler treatment. Silane-coated ATH caps the surface hydroxyls; stearate-coated ATH mainly improves dispersion and melt flow. Both are sold as “surface treated” and the price difference is small, so it is easy to buy the wrong one without noticing. For anything outdoor or wet, you want the silane route — it reduces the hydroxyl sites that both grab your HALS and pull in water. It is not a perfect cap; in practice not every hydroxyl reacts. But it moves the material from “will fail” to “will pass”.
Last, dispersion. UV protection from carbon black depends on dispersion as much as on loading. An agglomerated 2.5 % is worth less than a well-dispersed 2 %. If you are dosing on your own line rather than buying a finished flame retardant compound, this is where it goes wrong most often.
The trade-off table nobody puts in the datasheet
| Property | PE jacket | PVC jacket | LSZH / HFFR jacket | What it costs you |
|---|---|---|---|---|
| Density | ~0.92 g/cm³ | 1.4–1.5 g/cm³ | 1.50–1.57 g/cm³ | ~70 % more kg per km than PE. Quote per kg looks fine; cost per metre does not. |
| Elongation at break | 400–600 % | 200–300 % | 140–155 % | Almost no ageing margin. Bend radius and drum handling get tighter. |
| Tensile strength | ≥12 MPa | 12–18 MPa | ~11 MPa (ST8 floor: 9 MPa aged) | Pulling tension in long duct runs needs checking, not assuming. |
| UV / weathering | Excellent with 2 % CB | Good, but plasticiser migrates | Poor unless engineered | HALS adsorbed by the filler. Needs silane-treated filler + fine carbon black. |
| Water absorption | Very low | Low | High if filler untreated | Insulation resistance drops on wet ageing; tracking risk. |
| Processing ceiling | Wide | Wide | ATH ~200 °C / MDH ~330 °C | ATH grades cap your line speed. MDH costs more but opens the window. |
The density row is the one that catches purchasing. A quote comparison done per kilogram against a PVC compound is misleading by roughly the density ratio — and then the LSZH compound is more expensive per kilogram on top of that. Do the comparison per metre of finished cable or you will approve a number that is not the number.
A job that took four rounds
A fibre customer in the Gulf, aerial drop cable, wanted an LSZH jacket because the tender said halogen-free. They had a black HFFR grade already passing IEC 60332-1 comfortably. Their qualification called for ASTM G154 with UVA-340 lamps at 60 °C, with the usual criterion of retaining at least 50 % of tensile strength and elongation.
Round one died at roughly 600 hours — elongation had fallen from about 155 % to the low 60s, so under 50 % retention. Their first assumption, and honestly ours for the first week, was that the HALS loading was too low. Round two doubled it. The result barely moved. That is what told us it was adsorption rather than dosage; if you were simply short of stabiliser, doubling it would have bought you something.
Round three changed the ATH from a stearate-coated grade to a silane-coated one and cut the HALS back to its original level. Better, still marginal. Round four added 2.2 % carbon black at 20 nm in place of part of the organic UV package, and that one passed with room to spare.
Total elapsed time, about eleven weeks, most of it waiting on the weathering chamber. The customer was not happy about that and I do not blame them — they had budgeted three weeks for a “material change”. If your tender closes in a month and it needs a fresh 1000-hour weathering report, that timeline does not exist. Order the test before you order the cable.
Which weathering standard your customer actually means
This causes more confusion than it should, and it is worth getting right before you commit to a chamber booking. ISO 4892-2 and ASTM G154 are not the same test and not interchangeable.
| Standard | Light source | Its ASTM / ISO twin | Practical note |
|---|---|---|---|
| ISO 4892-2 | Xenon arc | ASTM G155 | Full-spectrum, closer to real sunlight. Slower, more expensive, usually 1000–2000 h. |
| ISO 4892-3 | Fluorescent UV | ASTM G154 | UVA-340 or UVB lamps. Harsher in the short-wave region, cheaper, faster. |
| IEC 60754-2 | — | — | pH ≥4.3, conductivity ≤10 µS/mm — but these sit in Annex A as recommended, not normative. |
| IEC 61034 | — | EN 50268 | ≥60 % light transmittance in the 3 m cube. Unrelated to weathering — see the smoke density test breakdown. |
A G154 pass does not automatically buy you an ISO 4892-2 pass, and if your customer’s spec names one, the report has to name that one. We have seen a perfectly good report rejected purely because it was the wrong lamp.
One more on IEC 60754-2: the pH 4.3 and 10 µS/mm figures everyone quotes as hard limits are recommended performance requirements in Annex A. If a customer writes them into a contract as pass/fail, that is their choice to make — just know that the standard itself frames them as guidance. The same care applies when comparing LSZH vs PVC jacket specifications, where the two families are often judged against criteria that were never written for both.
Thermal stability and the line-speed question
“Thermal stability” in an LSZH enquiry usually means one of two different things, and it is worth asking which.
If they mean processing, the answer is the filler decomposition onset: ATH begins releasing water around 200 °C, MDH around 330 °C. Run an ATH-filled compound too hot or too long in the barrel and you get porosity and surface defects — the filler is doing its job at the wrong moment. That is the practical ceiling on your line speed, and it is the main reason to pay for MDH.
If they mean service life at elevated temperature, that is long-term thermal ageing, a different test and a different formulation lever — antioxidant package rather than filler chemistry. We cover the mechanism of that decay in flame retardant aging.
Buyers frequently write one and mean the other. Getting that clarified in the first email saves a sample round.
What we would suggest you do
If your cable is indoors, in trays or risers, never wet, never in daylight: do not buy a UV-engineered grade. A standard halogen-free flame retardant package is enough, and you would be paying a premium for a property the installation never exercises. Say no to us on this one.
If any part of the run is outdoor, aerial, or in a duct that floods: put three things in the specification, not one. Silane-treated filler, carbon black at 2 %+ with primary particle size stated, and the named weathering standard with lamp type. “UV resistant” on its own is not a specification and every supplier will happily tick it.
If you compound on your own line: the filler treatment is your decision and your leverage. Buy the silane-coated grade for outdoor work even though the stearate grade extrudes a little more easily. Our flame retardant additives line covers both coatings and we will tell you which one your application needs, including when the cheaper one is fine.
If you extrude but do not compound: buy the finished compound and make weathering a specification line item with a report attached, not a conversation. A flame retardant masterbatch route can work for the flame package but is a poor way to deliver 60 % filler — at that loading you want a compound.
Before you commit to a tender date: count the weathering test into the schedule. 1000 hours is roughly six weeks in the chamber before anyone writes a report.
FAQ
Is there such a thing as a genuinely UV-resistant LSZH compound?
Yes, but it is a specific engineered grade, not a property that standard HFFR has. It needs silane-treated filler, correctly specified carbon black, and a stabiliser package chosen knowing the filler will compete for it. Expect to pay a premium over a standard indoor jacket grade, and expect the qualification to take longer.
Why is my LSZH compound so much heavier than PVC?
Because 55–65 % of it is mineral. Typical HFFR density is 1.50–1.57 g/cm³ against roughly 1.4–1.5 for PVC and 0.92 for PE. Compare quotations per metre of finished cable rather than per kilogram of compound, or the comparison is meaningless.
Can I improve UV performance just by adding more HALS?
Usually not, and that is the counter-intuitive part. The metal hydroxide filler adsorbs the stabiliser, so extra loading largely disappears onto the filler surface. Changing the filler coating, or shifting protection to carbon black, gives more per dollar. Doubling HALS with no improvement is actually a useful diagnostic.
What does silane treatment cost compared to stearate?
The gap is modest at compound level — small enough that it should not drive the decision for outdoor cable, and small enough that suppliers sometimes substitute without flagging it. Ask for the coating type on the COA, not just “surface treated”.
Does a UV grade change my flame test results?
Carbon black is essentially neutral to slightly helpful for char. Changing filler coating can shift dispersion enough to move the burn result at the margin, so if you were passing IEC 60332-3 narrowly, re-run it after the change. Do not assume the fire result carries over.
Can Rectivas issue the UL or weathering certificate?
No. We are a sourcing and technical partner, not a factory owner and not a laboratory. We arrange UL94 and LOI screening at our partner factory’s lab for fast selection work, and third-party weathering and cable-standard reports through an accredited laboratory. The certificate is issued in the testing body’s name against the manufacturing factory — never ours, and you should be suspicious of any trading partner who claims otherwise.
What is your MOQ and lead time on an outdoor LSZH grade?
Trial quantities for line qualification are small and quick. Production quantities depend on which factory the formulation suits — we source from ISO 9001 certified factories rather than running one line, so the honest answer is that we confirm after we see your specification. Send the standards list, the elongation minimum, and your line speed.
Final thoughts
LSZH is a fire-safety material that happens to be sold as a jacket. The chemistry that makes it safe — a very high mineral loading — is the same chemistry that makes it fragile in sunlight and thirsty in water. Nobody designed it to be a weathering material, and treating “UV resistant” as a checkbox rather than an engineered specification is where most outdoor projects go wrong. Tell us where the cable lives before you tell us which grade you want; that one sentence changes the recommendation more than anything else on the enquiry form. Our flame retardant for wire and cable overview maps the rest of the standards, and the full list of halogen-free flame retardants covers what else can carry the load when ATH cannot. How the coating actually gets onto the particle, and why surface moisture decides whether it bonds, is covered in the LSZH compound production process. Coating is only one of three filler decisions; mineral choice and grade specification come first, in flame retardant fillers compared.
—— Rectivas Materials 团队 技术工程师老陈