Quick answer: This is a working glossary of the terms that appear on flame retardant datasheets, enquiries and specifications — grouped by where you meet them rather than alphabetically, with the common misreading noted for each. The five most frequently confused: RoHS is not halogen-free, LOI is not a certification, a rating is not a material property, PLC 0 is the best not the worst, and a Yellow Card covers compounds, not additives.
We wrote this because of enquiries like this one, which arrived more or less verbatim: “RoHS halogen-free V0 grade, high LOI, need UL certificate.” Four requirements, and three of them do not mean what the sender thought. RoHS permits most brominated flame retardants. V-0 is meaningless without a thickness. LOI is not a certificate and no standard in their market required it. Quoting that enquiry literally versus quoting what they actually needed differed by roughly a factor of three in price.
Ratings and Classes
What a material is graded as. Note that every one of these belongs to a specific test on a specific specimen — they are not interchangeable, as set out in the standards comparison.
| Term | What It Means | Where People Get It Wrong |
|---|---|---|
| V-0 / V-1 / V-2 | UL94 vertical burn classes. V-0: ≤10 s afterflame per application, ≤50 s total over ten applications, no drips igniting cotton | ⚠️ V-1 and V-2 have identical time limits — only dripping separates them. And no rating is valid without a stated thickness |
| HB | Horizontal burning; ≤40 mm/min at 3–13 mm, ≤75 mm/min below 3 mm | ⚠️ Many unmodified plastics already pass. If your drawing says HB you may need no flame retardant at all |
| 5VA / 5VB | Larger-flame enclosure ratings. 5VA is the highest UL94 class | The only difference: 5VB allows a burn-through hole, 5VA does not |
| VTM-0 / -1 / -2 | The thin-material version, specimen wrapped on a 12.7 mm mandrel | A film cannot be “V-0” — it is VTM-0. Treat a V-0 film claim as a question |
| LOI | Limiting oxygen index: minimum O₂% sustaining combustion. Air is 20.9% | ⚠️ A development metric, not a certification — except in rail, GB supply chains and some cable tenders where it is contractual |
| FSI / SDI | Flame Spread Index / Smoke Developed Index from ASTM E84. Class A = FSI 0–25 and SDI ≤450 | Both thresholds are mandatory. Halogenated systems often pass FSI and fail on smoke |
| Euroclass (EN 13501-1) | A1, A2, B, C, D, E, F for construction products, plus s1–s3 smoke and d0–d2 droplets | “Class B” alone is not a specification. It must read like B-s1,d0 |
| GB 8624 | China’s construction product classes: A, B1, B2, B3 | ⚠️ B1 is not Euroclass B. Four classes vs seven, no official mapping |
| HL1 / HL2 / HL3 | EN 45545-2 rail hazard levels. HL3 requires LOI > 32 | Rail clauses get copied onto non-rail parts, which multiplies cost for nothing |
| CPR Euroclass (cable) | Aca to Fca for cables in EU construction works | A separate scale from the EN 13501-1 letters despite looking similar |
| CMP / CMR / OFNP / OFNR | NEC cable listings (plenum / riser), earned via NFPA 262 and UL 1666 | ⚠️ Plenum-rated does not mean halogen-free — most plenum cable is fluoropolymer |
Electrical Properties
The requirements a burn rating says nothing about. For electronics these usually decide the formulation — see flame retardant for electronics.
| Term | What It Means | Where People Get It Wrong |
|---|---|---|
| CTI | Comparative tracking index (IEC 60112): voltage a surface resists before forming a conductive carbon path | Not a fire test at all. Brominated + antimony systems typically track worse |
| PLC | Performance level category, 0–5, from the CTI result | ⚠️ PLC 0 is the best (≥600 V), not the worst. Lower number = stronger, same as on a Yellow Card |
| GWIT | Glow wire ignition temperature (IEC 60695-2-13). ≥775 °C clears unrestricted use in current-carrying appliance parts | ⚠️ V-0 does not predict it. UL94 removes the flame; glow wire keeps the heat on |
| GWFI / GWT | Glow wire flammability index (>850 °C typical) / glow wire test on the finished part (750 °C, ≤2 s) | GWT is tested on your part, not on a plaque — a different obligation |
| RTI | Relative thermal index: long-term temperature capability, separate electrical and mechanical values | Ignored at design stage, then decides whether the part survives ten years |
| HWI / HAI | Hot wire ignition / high-current arc ignition (UL 746A) | Set by the electrical function of the part, not by the resin family |
Chemistry and Abbreviations
The acronyms on a technical datasheet. Each links to the detail where we have it.
| Abbreviation | Full Name | Typical Use and Caveat |
|---|---|---|
| ATH / MDH | Aluminium trihydroxide / magnesium dihydroxide | Mineral, works by heat absorption. Needs 55–65% loading. ATH decomposes ~200 °C, MDH ~330 °C — the reason MDH goes into PP and PA |
| APP | Ammonium polyphosphate | Acid source in intumescent systems. Calcium carbonate in the same formulation will neutralise it |
| MCA | Melamine cyanurate | ⚠️ Excellent in unfilled nylon, close to useless once glass fibre stops the dripping it relies on |
| MPP | Melamine polyphosphate | Common partner to phosphinate in glass-filled polyamide |
| DEPAL / OP | Aluminium diethylphosphinate | Mainstream halogen-free route for reinforced PA and PBT; supports high CTI |
| DOPO | 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide | Reactive phosphorus, bonded into epoxy. The halogen-free laminate workhorse |
| BDP / RDP / TPP | Bisphenol-A / resorcinol / triphenyl phosphate | Liquid phosphate esters for PC and PC/ABS. TPP is the most volatile, BDP the most hydrolysis-resistant |
| EG | Expandable graphite | Expands into an insulating worm. Particle size dictates whether it survives your process |
| KSS | Potassium diphenyl sulfone sulfonate | Used at very low dose in transparent PC where clarity must survive |
| DBDPE | Decabromodiphenyl ethane | The mainstream PBDE replacement. RoHS compliant, but inside the scope ECHA is preparing a restriction on |
| TBBPA | Tetrabromobisphenol A | Highest-volume BFR worldwide. Mostly reactive in laminate, which changes its regulatory position |
| PBDE / HBCD | Polybrominated diphenyl ethers / hexabromocyclododecane | ⚠️ Banned as POPs. Still turn up in recycled feedstock |
| Sb₂O₃ | Antimony trioxide | Synergist for halogen systems — not a flame retardant alone. IARC 2B classified |
| Zinc borate / stannate | Antimony replacements and char promoters | Buy char quality and smoke suppression, not much LOI |
| PTFE (anti-drip) | Fibrillating polytetrafluoroethylene | ⚠️ Under 1% does nothing for LOI and is often what wins V-0 — it fixes dripping, not flammability |
| Intumescent | Acid source + carbon source + blowing agent that swell into a foamed char | Sensitive to anything alkaline in the formulation |
| Gas phase / condensed phase | Interrupting flame chemistry vs building a protective char | Explains why gas-phase systems pass UL94 but not glow wire |
| Candlewick effect | Glass fibres wicking molten polymer to the flame | Why reinforced grades need more flame retardant, not less |
Standard Numbers You Will Meet
Worth separating these out, because a recurring confusion is treating a test method as if it were a requirement. A method tells you how to measure; the required value comes from a product standard or a customer specification.
| Number | What It Is | Method or Requirement? |
|---|---|---|
| UL 94 / IEC 60695-11-10 / GB/T 2408 | Horizontal and vertical burning of plastics — the same test in three numbering systems | Method |
| ASTM D2863 / ISO 4589-2 / GB/T 2406 | Limiting oxygen index | Method |
| ASTM E84 | Steiner tunnel, 25-foot flame spread | Method — Class A comes from the building code, not from E84 |
| EN 13501-1 / GB 8624 | Reaction-to-fire classification for construction products | Requirement (classification systems, not equivalent to each other) |
| IEC 60112 | Comparative tracking index | Method (UL 746A assigns the PLC) |
| IEC 60695-2-11 / -2-12 / -2-13 | GWT (finished part) / GWFI / GWIT | Method — IEC 60335-1 sets the values for appliances |
| IEC 60332-1 / -3 | Cable flame propagation, single wire / bunched in a tray | Method |
| IEC 61034 / IEC 60754 / IEC 60331 | Smoke density (3 m cube) / acid gas / circuit integrity in fire | Method — the three clauses beyond propagation |
| NFPA 262 / UL 1666 | Plenum and riser cable fire tests behind NEC listings | Method |
| FMVSS 302 / ISO 3795 | Vehicle interior horizontal burn, ≤102 mm/min | Requirement (and a low one) |
| EN 45545-2 | Rail vehicle fire behaviour, hazard levels HL1–HL3 | Requirement |
| IEC 62368-1 / IEC 60335-1 | Safety standards for AV/IT equipment and household appliances | Requirement — they invoke the methods above |
Regulatory Terms
| Term | What It Means | Where People Get It Wrong |
|---|---|---|
| RoHS | EU restriction of ten substance groups in electrical equipment | ⚠️ Only two are brominated (PBB, PBDE). DBDPE, TBBPA and brominated PS are all RoHS compliant. RoHS ≠ halogen-free |
| IEC 61249-2-21 | The actual halogen-free definition: Br ≤900, Cl ≤900, total halogen ≤1500 ppm | This is the number to specify when you mean halogen-free. Not a fire test |
| REACH / SVHC | EU chemicals regulation / substances of very high concern candidate list | Registration duty falls on the EU importer, not the Chinese supplier |
| POPs / UTC | Persistent organic pollutants / unintentional trace contaminant limit | ⚠️ PBDE UTC is now 10 mg/kg general, but 350 mg/kg for recycled content, falling to 200 in Dec 2027 |
| Yellow Card | UL’s listing for a recognised plastic material, stating grades, colours and thicknesses evaluated | ⚠️ Issued for compounds, not additives. No additive supplier can give you one |
| Recognized vs Listed | Component recognition vs a finished-product listing | Buying recognised material does not make your device listed |
Commercial and Processing Terms
| Term | What It Means | Practical Note |
|---|---|---|
| phr | Parts per hundred resin | ⚠️ Not the same as weight percent. 20 phr ≈ 16.7 wt% — a real source of dosing errors |
| Let-down ratio | How much masterbatch you add per unit of base resin | Compare masterbatches on active content, never on price per kilo |
| Additive / masterbatch / compound | Powder, pellet concentrate, ready-to-run material | Above roughly 40–50% loading, compound usually beats dosing on your own line |
| Carrier resin | The polymer holding the additive in a masterbatch | It is up to a third of what you buy, and it ends up in your part |
| Blooming / plate-out / migration | Additive surfacing on the part / depositing on tooling / leaving the matrix over time | All three point at the same thing: something is mobile in your formulation |
| PCR | Post-consumer recycled material | WEEE-origin PCR carries legacy POPs risk; screen before formulating |
| TDS / SDS / COA | Technical data sheet / safety data sheet / certificate of analysis | Only the COA is lot-specific. The other two describe the product in general |
| LSZH / LS0H / LSF | Low smoke zero halogen — a cable compound class, usually mineral-filled polyolefin | ⚠️ A material category, not a rating. “LSZH” on its own does not tell you which IEC clauses it passes |
| MFI / MFR | Melt flow index / rate — how easily the melt flows | High filler loading drops it hard; thin-wall parts need flow and high loading at once, which is the core tension |
| Char yield | Residue left after burning — the protective layer condensed-phase systems rely on | What glow wire and large-scale tests reward, and what gas-phase chemistry does not build |
| Smoke density | Light obscuration by smoke (IEC 61034 for cable, SDI within ASTM E84) | The clause that most often fails an otherwise passing halogenated formulation |
| MOQ | Minimum order quantity | Ask separately for trial quantity — sampling and production MOQ are different conversations |
The Five That Cost the Most
If you take only one thing from this page, take these — they are the misreadings that turn into wrong quotes, failed certifications and wasted development cycles.
- RoHS compliant is not halogen-free. Different requirements, and a RoHS certificate tells you nothing about halogen content.
- A rating is not a material property. V-0 belongs to a material at a thickness in a colour. “Our material is V-0” is an incomplete sentence.
- LOI is not a certification unless a specification names it — and in rail and parts of the Chinese market, it does.
- PLC 0 is the best CTI category, not the worst. Low numbers mean strong performance here.
- A Yellow Card covers compounds, not additives. Asking an additive supplier for one has no valid answer.
Get an enquiry right on those five and most of the back-and-forth disappears. Send us the clause rather than the paraphrase, with the thickness and the colour, and we can usually answer in one reply instead of four.
—— Rectivas Materials 团队 技术工程师老陈