Flame-Retardant Plastics: UL 94 Ratings and FR Systems by Polymer (13 Plastics Compared)

Flame-retardant plastics are polymers compounded with a flame-retardant system so that a part reaches a fire class such as UL 94 V-0 at a stated thickness, using from about 15 wt% of a phosphinate blend in glass-filled nylon to 160-180 phr of mineral filler in a halogen-free cable compound. Most plastics burn in air without help, because polypropylene needs only 17.5 to 17.8 vol % O2 to keep burning; so which plastics resist fire on their own, and which rating can the flame-retardant grade of each one reach?

Flame retardants make up 13 % of all plastic additives by weight, and a fire class always belongs to the compound, not to the polymer name. Those compounds exist for a measured reason: in a 1988 room-burn test at the US National Bureau of Standards (NBS), flame-retarded products gave more than 15 times the available escape time of untreated ones and released a quarter of their heat.

This page starts from the plastic, not from the additive: what a flame-retardant plastic is, how a plastic burns, which plastics resist fire unmodified, and 13 plastics compared by the UL 94 rating, thickness and flame-retardant system of their FR grades, followed by how ratings are assigned, what flame retardancy costs, a 6-step specification, the rules on the flame retardant inside the part and the supply routes. The chemistry of each additive class is compared on the hub flame retardants for plastics.

Four figures that define flame-retardant plastics

• 13 plastics compared: from polypropylene and PVC through polycarbonate, nylon and PBT to the inherently flame-resistant PPS, PEEK, PEI and PSU
• 17.5-17.8 vol % O2: the limiting oxygen index of unmodified polypropylene, below the about 21 vol % oxygen of air
• 25-29 vol % O2: the limiting oxygen index of unmodified polycarbonate, which rates UL 94 HB to V-2 without additives
• 0.4-3.2 mm: the thickness range over which glass-filled PA6 and PA66 with 15-20 wt% Exolit OP 1312 rate UL 94 V-0

What Is a Flame-Retardant Plastic?#

A flame-retardant plastic is a polymer grade that ignites later, spreads flame more slowly and stops burning sooner than its base resin, because a flame retardant has been blended into it, built into its chain or added as a second polymer. The flame retardant in it is a substance added to or reacted into a polymer to suppress, reduce, delay or modify the spread of flame; it moves the plastic up a test classification but does not make it non-combustible. Datasheets use trade synonyms such as "fire-retardant plastic", "FR grade", "PP-FR" and "PC-FR"; "flame retardant" is the usual term for plastics, "fire retardant" for coatings, wood and sheeting. A plastic becomes flame retardant in 3 ways.

• Additive flame retardants: blended into the melt without bonding to the polymer, such as aluminium trihydrate (ATH), DBDPE and triphenyl phosphate (TPP)
• Reactive flame retardants: built into the polymer chain, such as TBBPA in FR-4 epoxy laminates, DOPO in epoxy resins and phosphorus-containing PET
• Polymeric flame retardants: high-molecular-weight polymers in their own right, such as brominated polystyrene, PolyFR and poly(pentabromobenzyl acrylate)

The route decides how permanently the flame retardant stays in the part, and the line between the first two routes is defined under reactive vs additive flame retardants.

Can plastic be fire retardant?#

Yes: plastic can be made fire retardant, and polypropylene, which keeps burning at only 17.5 to 17.8 vol % oxygen, reaches UL 94 V-0 with 21 wt% of a piperazine pyrophosphate (PAPP) and melamine polyphosphate (MPP) blend. That PAPP:MPP blend, at a 2:1 ratio, rated V-0 in both virgin and recycled polypropylene in a 2026 study in ACS Applied Polymer Materials (thickness not stated in the source). An intumescent PP/IFR compound of the same polymer reaches a limiting oxygen index of 29-33 vol % O2.

Making plastic fire retardant is a compounding step: the flame retardant is dosed into the polymer melt at the compounder, or added as a concentrate at the moulding machine. Fire-retardant sprays and coatings are coating products, not plastic additives. If additives can lift polypropylene that far, does a flame-retardant plastic still burn? Yes, in a large enough fire: a fire class describes the behaviour of a plastic under a defined ignition source, not immunity to fire.

Inherently flame-resistant plastics vs flame-retardant grades#

Inherently flame-resistant plastics such as PPS, PEEK, PEI and PSU resist fire because of their polymer backbone, while flame-retardant grades of PP, PC, ABS or nylon resist fire because a flame retardant has been added to a polymer that would otherwise burn. The two words carry the difference: "retardant" names an additive or treatment, "resistant" names a property of the material itself, as in PEEK, PPS and aramid. Reactive flame retardants sit between the two, because they turn the polymer into a chemically modified, flame-retarded backbone. Table 1 compares the 3 routes to a fire-resistant plastic part.

PVC belongs to the inherent group for a chemical reason: the polymer is 57 % chlorine by mass. Polycarbonate stands in between, rating UL 94 HB to V-2 without additives but needing a flame retardant for V-0. The high-performance group pays for its inherent behaviour in price and processing heat: PEEK has a glass transition temperature of 143 °C and melts at 343 °C, and PPS has a maximum service temperature of 240 °C. Aramid, the other inherently flame-resistant material the research names, enters plastics as a reinforcing fibre, covered under aramid fibres in plastics.

Is flame-retardant plastic the same as fireproof?#

No: a flame-retardant plastic still burns in a large enough fire; the flame retardant only moves it up a test classification, for example from a polypropylene that keeps burning at 17.5 vol % oxygen to a compound whose specimens stop flaming within 10 s in the UL 94 vertical test. No plastic additive makes a polymer non-combustible, so "fireproof" is not a property of any plastic class. The same caution applies to oxygen index claims: an LOI above the 21 vol % O2 of air marketed as "self-extinguishing" is misleading, because the test burns a small specimen in a controlled atmosphere, not a part in a room fire.

How Does a Plastic Burn, and What Makes It Flame Retardant?#

A plastic burns in a 5-step cycle: heat breaks the polymer into combustible gases, the gases mix with air and burn in the flame, and part of the flame's heat flows back into the plastic to make more fuel; a plastic is flame retardant when it, or an additive in it, breaks that cycle early enough to pass its fire test. A flame retardant breaks the cycle in the condensed phase, the solid or molten plastic, where it cools the melt or builds char, or in the gas phase, where it interrupts the flame chemistry. Phosphorus acts in both: Bernhard Schartel at the German Federal Institute for Materials Research and Testing (BAM) showed in 2010 in Materials that phosphorus flame inhibition lowers combustion efficiency and raises the carbon monoxide yield of the fire. Four burning attributes decide which class a plastic reaches.

• Oxygen demand: the limiting oxygen index (LOI), the minimum oxygen in an oxygen and nitrogen mixture that just supports flaming (ASTM D2863-23e1, ISO 4589-2), against about 21 vol % O2 in air
• Melt dripping: flaming drips that ignite cotton fail UL 94 V-0 and V-1; polypropylene drips and forms no char
• Char formation: a carbon layer that holds fuel back, which polycarbonate builds on its own
• Heat release: peak and total heat release rate (pHRR, THR) in the cone calorimeter, 1148-1332 kW/m2 peak for neat polypropylene at 35 kW/m2

Glass fibre adds a fifth effect: the fibres wick molten polymer back to the flame, the candle-wick effect, so glass-filled grades need more flame retardant than unfilled ones. How each additive class breaks the burning cycle, in the gas phase or in the solid, is explained under how flame retardants work.

Which Plastics Are Flame Retardant Without Additives?#

Only 2 groups of plastics resist fire without additives: polymers whose backbone carries chlorine or aromatic links, such as PVC (57 % chlorine by mass), PPS, PEEK, PEI and PSU, and polycarbonate, which rates UL 94 HB to V-2 unmodified with a limiting oxygen index of 25 to 29 vol % O2. Every other common plastic, from polypropylene and polyethylene to polystyrene, ABS and nylon, burns once ignited and needs a flame retardant for a V class. Table 2 sets out the unmodified fire behaviour of the 13 plastic groups compared on this page, with the 4 oxygen index values this reference holds from a sourced measurement.

Footnote: Only 4 unmodified plastics have a sourced LOI in this reference; LOI values without a stated thickness and method are not comparable.

Ranked by sourced oxygen index, unmodified plastics climb from polypropylene at 17.5-17.8 vol % O2, below the oxygen in air, to EPS foam at about 18 vol % O2, PA6 at 21.0 vol % O2, level with air, and polycarbonate at 25-29 vol % O2, the only one of the 4 above air. EPS at about 18 vol % O2 falls short of the ASTM C578 requirement of more than 24 vol % O2 for insulation board. This reference holds no sourced LOI for PVC, PE, PS, ABS, PMMA, POM, PTFE, PEEK or PSU and does not estimate one. The method behind these oxygen index values is on limiting oxygen index (LOI).

If polycarbonate already rates V-2, why do PC housings still carry a flame retardant? A V-2 rating allows flaming drips that ignite the cotton, while V-0 forbids them and limits each afterflame to 10 s, and polycarbonate reaches that class at thin walls only with a charring catalyst such as a sulfonate salt plus a PTFE anti-drip agent. Flexible PVC follows the same logic: cable compounds still need ATH and a synergist to reach UL 94 V-0 at 3 mm.

Flame-Retardant Plastics by Polymer: 13 Plastics and the UL 94 Rating Each Reaches#

The 13 plastics most often supplied as flame-retardant grades are polypropylene, polyethylene and EVA, PVC, polystyrene, ABS, polycarbonate, PC/ABS, nylon, PBT and PET, TPU and TPE, epoxy, polyurethane foam and the inherently flame-resistant high-performance plastics, and the thinnest verified V-0 rating among them is 0.4 mm for glass-filled nylon and PBT. Table 3 lists the rating each FR grade reaches, its thickness, the flame-retardant system, the loading with its basis, the main trade-off and the source type, in the same order as the 13 sections below.

Footnote: Loadings are supplier or study examples, not universal values; the rating has to be confirmed on the actual part thickness and colour.

Which number in Table 3 matters most when two grades both say V-0? The thickness comes first and the colour second, because a rating holds only at or above the thickness tested and is listed by colour, as the rating section below explains. A V-0 grade also carries more than its flame retardant: antioxidants, lubricants, glass fibre and colorants share the formulation, and each polymer's full additive package is set out under additives by polymer.

1. Flame-retardant polypropylene (PP-FR)#

Polypropylene is not flame retardant on its own, because it keeps burning at 17.5 to 17.8 vol % oxygen and drips without forming char, but flame-retardant PP (PP-FR) reaches UL 94 V-0 with 21 wt% of a PAPP and MPP blend or 22-30 wt% of an APP-based intumescent system. Intumescent systems supply the char that polypropylene cannot form by itself, with ammonium polyphosphate (APP) as the acid source and pentaerythritol as the carbon source. PP-FR therefore mostly relies on intumescent flame retardants, and Clariant's APP grades Exolit AP 750 and AP 766 process up to about 220 °C. A char catalyst helps: 0.25 wt% zinc oxide or manganese oxide in an APP and pentaerythritol compound gave an LOI of 30 vol % O2 with V-0, and 1.5 wt% zinc oxide reached 43.7 vol % O2 (Polymers, 2025).

In the cone calorimeter at 35 kW/m2 on 100 x 100 x 3 mm plaques (ISO 5660-1), an intumescent package cuts the peak heat release rate of polypropylene from 1148-1332 kW/m2 to 220-255 kW/m2. Polypropylene is sold in 4 flame-retardant routes, ordered from the highest rating down.

• Intumescent PP-FR: APP or PAPP/MPP systems for UL 94 V-0 at 21-30 wt%
• Brominated PP-FR: a brominated flame retardant such as DBDPE with antimony trioxide for V-0
• FR-370 PP: tris(tribromoneopentyl) phosphate (CAS 19186-97-1) for UL 94 V-2 in moulded parts and fibres
• Mineral-filled PP: coated MDH at up to 65 wt% for halogen-free, low-smoke compounds; Huber's HFFR PP reference uses 185.7 phr MDH for an LOI of 30.2 vol % O2

ATH is rarely used in polypropylene, because PP processing runs above its water-release onset of about 200 °C, which is why the mineral route uses magnesium hydroxide. Loadings, synergists and the V-2 route are compared on flame retardants for polypropylene.

2. Flame-retardant polyethylene and EVA#

Flame-retardant polyethylene and EVA are mostly halogen-free cable compounds filled with 160-180 phr of aluminium trihydrate or magnesium hydroxide, about 61.5 wt% of the compound at 160 phr, because unfilled EVA/LLDPE peaks above 550 kW/m2 of heat release in the cone calorimeter at 35 kW/m2. The fillers work by mass: aluminium trihydrate (aluminum trihydrate, ATH) and magnesium hydroxide (MDH) absorb heat, release water and delay ignition by 120-160 s against the unfilled polymer. Cable makers sell these compounds as LSZH (low smoke zero halogen), also written LSF, LS0H, LSOH, HFFR, ZHFR, NHFR or OHLS. Huber's halogen-free reference formulation shows how a polyethylene and EVA cable compound is built in parts per hundred of resin (phr).

Why ATH in one cable and MDH in another? Processing temperature decides: ATH releases water from about 200 °C and absorbs 1051 J/g, while MDH is stable to about 320 °C, absorbs 1316 J/g and processes about 110 °C higher. Silane-crosslinked polyethylene takes 180 phr of vinyl-silane-coated ATH, and halogen-free compounds such as these meet acidity class a1 under EN 60754-2 (conductivity below 2.5 µS/mm, pH above 4.3). CPR classes and PVC cable systems are compared on flame retardants for wire and cable.

3. Flame-retardant PVC#

PVC is the one commodity plastic that brings its own flame retardant, because the polymer is 57 % chlorine by mass, yet flexible PVC cable still needs 45-100 phr of ATH and 5 phr of zinc borate to reach a limiting oxygen index of 26-27 vol % O2 and UL 94 V-0 at 3 mm. Huber's cable formulation behind those figures uses PVC K70 100 phr, the plasticizer DIDP 55 phr, a lead-free stabilizer 2.7 phr, ATH 45-100 phr, zinc borate 5 phr and chalk 10 phr, against a minimum LOI of 26 vol % O2 for PVC cable insulation. Chlorinated PVC (CPVC) carries 56.7-74 % chlorine. Flexible PVC reaches its cable fire targets with 4 additive types.

• Antimony trioxide: a synergist with the polymer's own chlorine, used at 5 phr alongside 50 phr ATH in Huber comparison formulations
• Aluminium trihydrate: a cooling filler at 45-100 phr
• Zinc borate and zinc hydroxystannate: smoke and drip reducers at 3-6 phr and 3-5 phr (ZHS in research formulations)
• Molybdates: smoke suppressants such as molybdenum trioxide and ammonium octamolybdate

The plasticizer type also shifts the oxygen index of flexible PVC. PVC releases hydrogen chloride when it burns and therefore cannot meet the EN 60754-2 acidity class a1, which is why LSZH cables use polyolefins instead. Stabilizers, plasticizers and fillers around the flame retardant are on additives for PVC, and the smoke suppressants have their own guide, flame retardants and smoke suppressants for PVC.

4. Flame-retardant polystyrene: HIPS, EPS and XPS#

Flame-retardant polystyrene comes in 2 forms: HIPS housings that reach UL 94 V-0 at 0.8 mm with 10.7 wt% bromine and 5 wt% antimony trioxide, and EPS or XPS insulation foams that must be lifted from a limiting oxygen index of about 18 to above 24 vol % O2 with a polymeric brominated flame retardant. HIPS housing grades deliver that bromine with about 8-12 wt% DBDPE (Albemarle Saytex 8010), and DBDPE has been a Substance of Very High Concern since 5 November 2025 (vPvB) but is not restricted. Halogenated HIPS has also lost one market: Ecodesign Regulation (EU) 2019/2021 has banned halogenated flame retardants in the enclosures and stands of electronic displays since 1 March 2021.

EPS and XPS insulation has already changed its flame retardant once. HBCD (CAS 25637-99-4) became an SVHC on 28 October 2008, reached its REACH Annex XIV sunset date on 21 August 2015 and entered Stockholm Convention Annex A in 2013, and the foams moved to PolyFR, a brominated butadiene-styrene copolymer (CAS 1195978-93-8) sold as Emerald Innovation 3000 (LANXESS), FR-122P (ICL) and GreenCrest (Albemarle). PolyFR belongs to the polymeric flame retardants, and the foam needs it because it is 95-98 % air, so flame spreads fast across it. The HBCD-to-PolyFR switch is detailed on flame retardants for polystyrene, EPS and XPS.

5. Flame-retardant ABS#

Flame-retardant ABS (FR-ABS) reaches UL 94 V-0 at 0.8 mm mainly with brominated systems, such as 10.7 wt% bromine from DBDPE plus 5 wt% antimony trioxide, because halogen-free routes are hard in ABS: RDP alone did not rate ABS at 20-30 wt% in one comparative study. That study, published in ACS Omega, found the same failure in EVA. FR-ABS is made in the 3 ways listed below.

• Brominated FR-ABS: DBDPE, FR-245 (TTBP-TAZ, CAS 25713-60-4, 67 % bromine) or additive TBBPA, each with antimony trioxide, and with a PTFE anti-drip agent in FR-245 housings
• Halogen-free research grades: APP with aluminium diethylphosphinate at 20 wt% in a 2024 study in Polymers (rating not stated)
• PC/ABS blends: a switch of polymer to a PC/ABS blend with an aryl phosphate

Why is halogen-free FR-ABS moving to PC/ABS? ABS, with a glass transition of about 105 °C, has no polycarbonate phase to build char, and the halogenated route is narrowing: the EU has barred halogenated flame retardants from display enclosures since 2021, and a REACH restriction of aromatic brominated flame retardants is in preparation. Brominated and halogen-free FR-ABS grades are compared on flame retardants for ABS.

6. Flame-retardant polycarbonate (PC-FR)#

Flame-retardant polycarbonate (PC-FR) needs only a trace of a sulfonate salt plus a PTFE anti-drip agent to move from its unmodified UL 94 HB to V-2 rating up to V-0, because PC already chars and has a limiting oxygen index of 25 to 29 vol % O2. Sulfonate salts migrate to the surface of the melt and catalyse crosslinking and charring of the polycarbonate, which has a glass transition of 147 °C, so the dosage stays very low; the research analogue KTSS reached V-0 at 0.02 % and is about 5 times more effective than KSS (thickness not stated). The PTFE anti-drip agent works alongside the salt, with patents citing 0.05-10 phr of active PTFE and 0.1 phr common in their examples.

Two salts compete for transparent and opaque PC housings, lighting covers and electrical parts. KSS (potassium 3-(phenylsulfonyl)benzenesulfonate, CAS 63316-43-8, EC 264-097-3) is fluorine-free, not an SVHC and not a PFAS, while PFBS-K (Rimar salt, Bayowet C4, CAS 29420-49-3) is a PFAS and has been an SVHC since 16 January 2020. Transparent PC options and salt dosages are on flame retardants for polycarbonate.

7. Flame-retardant PC/ABS blends#

Flame-retardant PC/ABS reaches UL 94 V-0 with about 20 wt% of an aryl phosphate and 0.4 wt% PTFE, as a 2024 study showed with the aryl bisphosphate BAPDP, but the phosphate plasticises the blend and pulls its heat deflection temperature down to 72.6 °C. The same 2024 PC/ABS compound reached an LOI of 25.4 vol % O2 (thickness not stated). The commercial aryl phosphates for the blend are BDP (CAS 5945-33-5; oligomer 181028-79-5; Fyrolflex BDP, ICL) and RDP (CAS 57583-54-7; oligomer 125997-21-9; Fyrolflex RDP).

Bernhard Schartel at the German Federal Institute for Materials Research and Testing (BAM) showed in 2010 in Materials that BDP acts mainly in the gas phase in PC and also adds char from the PC phase in PC/ABS. The EU ENFIRO project found a cost of that gas-phase route: RDP and BDP in styrenics gave more smoke. The older aryl phosphate TPP has been an SVHC since 7 November 2024 (endocrine disruption, environment), which pushes buyers to BDP and RDP. TPP, RDP and BDP are compared on organophosphate flame retardants, and the PTFE in the blend falls under the PFAS rules covered below.

8. Flame-retardant nylon: PA6, PA66 and high-temperature polyamides#

Flame-retardant nylon reaches UL 94 V-0 from 0.4 to 3.2 mm in glass-filled PA6 and PA66 with 15-20 wt% of an aluminium diethylphosphinate blend, a grade that also gives a glow-wire ignition temperature of 775 °C and a CTI of 600 V, while unfilled nylon can rate with melamine cyanurate alone. Unfilled PA6 sits at an LOI of 21.0 vol % O2, level with air, and melts at 215-218 °C, while PA66 melts at 264 °C. Unfilled PA6 and PA66 reach UL 94 V-0 with melamine cyanurate (CAS 37640-57-6) as the sole additive, a system that promotes melt dripping to carry heat away from the flame; this reference holds no verified loading for it. Unfilled and glass-filled grades are compared on flame retardants for nylon.

Glass fibre changes the system. Glass-filled PA6 and PA66 (10-50 % glass) wick the flame back into the part, so they need a phosphinate blend: Clariant's Exolit OP 1312 at 15-20 wt% rates V-0 from 0.4 to 3.2 mm with a GWFI of 960 °C, and glass-filled PA66 reaches hazard level HL3 under requirement R22 of the rail standard EN 45545-2. A 2026 study in Polymers measured a 15 wt% ADP-based system (ADP 12 wt% plus a P/N/Zn synergist 3 wt%) in PA6: LOI 30.7 vol % O2, V-0 at 3.2 mm and the cone results below. Red phosphorus reaches V-0 in glass-filled PA66 by charring but is limited to dark colours, and E&E manufacturers that have seen premature electrical failures avoid it; brominated polystyrene (Saytex HP-3010, HP-7010) and poly(pentabromobenzyl acrylate) (FR-1025) with antimony trioxide form the brominated alternative.

High-temperature polyamides such as PA 6T/66 reach V-0 at 1.6 and 0.8 mm with about 15 wt% of Exolit OP 1230. A high-temperature polyamide with OP 1230 also passed JEDEC J-STD-020C moisture sensitivity level 2 at a 260 °C peak reflow soldering profile. Heat stabilizers and lubricants for the same nylon grades are on additives for nylon.

9. Flame-retardant PBT and PET#

Flame-retardant PBT reaches UL 94 V-0 with 18 wt% of an aluminium diethylphosphinate grade, and glass-filled PBT with Exolit OP 1240 rates V-0 from 0.4 to 3.2 mm with a CTI of up to 600 V and no copper contact corrosion, which is why it is used for connectors and rail parts (EN 45545-2 R22 HL2). The 18 wt% grade is Clariant's Exolit OP 1260 (thickness not stated), and both grades belong to the phosphinate flame retardants (DEPAL). PBT melts at 223 °C and is sensitive to hot water above 60 °C, so its FR grades are chosen with hydrolysis in mind.

The brominated route for polyesters pairs brominated polystyrene with sodium antimonate instead of antimony trioxide, because sodium antimonate is less catalytically active towards polyester depolymerisation. PET fibres take a third route: a reactive phosphorus comonomer built into the PET chain. Fibre and film grades are on flame retardants for PBT and PET.

10. Flame-retardant TPU and TPE#

Flame-retardant TPU and TPE are mostly cable-jacket grades that carry 20-40 wt% of an aluminium diethylphosphinate system with synergists, a loading kept below that of mineral cable compounds so the jacket stays soft. Clariant names thermoplastic copolyester elastomers (TPC) and TPU for this system (rating not stated in the source), and the same phosphinate chemistry is listed for high-voltage connectors and cable insulation in electric vehicles. A mineral LSZH jacket carries about 60 wt% ATH, so the phosphinate route needs one third to two thirds of that flame-retardant mass. Jacket formulations are on flame retardants for TPU and TPE cable jackets.

11. Flame-retardant epoxy laminates and thermosets#

Flame-retardant epoxy laminates reach UL 94 V-0 with about 1-1.2 wt% phosphorus from reactive DOPO-type compounds in research formulations, replacing reactive TBBPA, which has carried a harmonised Carc. 1B classification since 1 September 2025. DOPO (CAS 35948-25-5) reacts into the epoxy network instead of sitting in it as a filler, and its derivatives work at 0.25-1.2 wt% phosphorus in a 2024 study in Polymers (thickness not stated). TBBPA (CAS 79-94-7), the reactive incumbent in FR-4 laminates, has been an SVHC since 17 January 2023 for carcinogenicity, and its Carc. 1B (H350) classification applies under Delegated Regulation (EU) 2024/197 (21st ATP). IEC 61249-2-21 defines halogen-free laminates; its limits are not verified in this reference.

Fillers add a condensed-phase share in thermosets. Boehmite (Apyral AOH, Nabaltec) goes into printed circuit board laminates, and ATH goes into unsaturated polyester and epoxy composites, where it cools the resin as it releases water. Laminate systems are compared on flame retardants for epoxy resins.

12. Flame-retardant polyurethane foam#

Flame-retardant polyurethane foam reaches UL 94 V-0 and a limiting oxygen index of 28-31 vol % O2 with expandable graphite, ammonium polyphosphate and a phosphorus polyol, while rigid PU and PIR insulation still widely uses the chlorinated phosphate TCPP. That expandable graphite package cut the peak heat release by 92 % (thickness not stated), and in a 2024 study in Polymers, 15 php of expandable graphite with 30 php of filler cut the peak heat release of a viscoelastic PU foam by 52 %. TCPP (CAS 13674-84-5; Fyrol PCF, Levagard PP) is not an SVHC and not restricted under REACH Annex XVII, DMPP is used at a typical 15 wt% in PUR, and flexible foam also uses melamine.

Furniture foam follows US state rules. California's TB 117-2013, effective in 2014, replaced the open-flame foam test with a smoulder test on the cover fabric, and California AB 2998 has banned halogenated and organophosphorus flame retardants above 1,000 ppm in juvenile products, mattresses and upholstered furniture since 1 January 2020. Expandable graphite turns the foam black, which limits it to foam where colour does not matter. Flexible and rigid foam systems are on flame retardants for polyurethane foam.

13. Inherently flame-resistant high-performance plastics: PPS, PEEK, PEI and PSU#

PPS, PEEK, PEI and PSU are the plastics that usually need no flame retardant at all, because their aromatic backbones make them inherently flame resistant, so their grades are built with glass fibre, mineral fillers and colorants instead. Their processing window explains the additive choice: engineering and high-performance plastics process at about 240-320 °C, above the water-release onset of ATH (about 200 °C) and of phase II APP (about 240 °C), so their packages hold glass fibre, mineral fillers, impact modifiers, nucleating agents, colorants and release agents rather than flame retardants. PEEK has a glass transition of 143 °C and melts at 343 °C, and PPS has a maximum service temperature of 240 °C.

Inherent does not mean unrated. The UL 94 class, thickness and colour still differ by grade, so a buyer reads the datasheet of each PPS, PEEK, PEI or PSU grade exactly as for a flame-retarded compound, and this reference publishes no rating for any of them until a grade-level source is verified. The trade-off of these high-performance polymers is price and processing heat, not fire behaviour. Glass fibre and colorant packages for these grades are on additives for high-performance polymers.

How Is the Flame Retardancy of a Plastic Rated?#

A plastic's flame retardancy is rated mainly by the UL 94 test, which classes a specimen from HB (slow horizontal burning) through V-2, V-1 and V-0 to 5VA, always at the thickness tested: glass-filled nylon with 15-20 wt% of a phosphinate blend, for example, is V-0 from 0.4 to 3.2 mm. The vertical test applies a 20 mm (50 W) flame twice for 10 s to 5 specimens of 125 x 13 mm, after conditioning for 48 h at 23 °C and 50 % relative humidity and for 7 days at 70 °C. UL 94 is harmonised as IEC 60695-11-10 and -20 and as ISO 9772 and 9773. Table 4 gives one line per class and the plastics in this reference that reach it.

Footnote: UL 94 is harmonised as IEC 60695-11-10 and -20 and ISO 9772 and 9773.

Why can two plastics with the same oxygen index get different UL 94 classes? LOI measures the oxygen a small specimen needs to keep burning in a candle-like test, while UL 94 measures afterflame time and flaming drips at a stated thickness, so dripping and charring separate plastics that share an LOI. That gap is also why an LOI above 21 vol % O2 marketed as "self-extinguishing" is misleading. The full test criteria, specimen conditioning and the foam and film classes are on UL 94 flammability ratings.

Thickness, colour and glass fibre: why a UL 94 rating belongs to one grade#

A UL 94 rating belongs to one thickness, one colour and one grade, because the test burns a specimen of a stated thickness: a glass-filled nylon listed V-0 from 0.4 to 3.2 mm says nothing about a 0.3 mm wall or about the unfilled grade of the same polymer. A UL 94 rating holds for the 3 conditions of the tested specimen listed below.

• Thickness: the thinnest wall of the part should sit at or above the rated thickness; the same glass-filled PA grade is V-0 across 0.4-3.2 mm, while HIPS data are given at 0.8 mm and PA 6T/66 data at 1.6 and 0.8 mm
• Colour: UL lists ratings by thickness and colour, so the colour of the part is part of the rating it can claim
• Glass fibre content and grade: glass fibre wicks the flame, so unfilled PA6 and PA66 can rate with melamine cyanurate alone while glass-filled grades need 15-20 wt% of a phosphinate blend

On the datasheet, a grade listed V-0 at 1.6 mm says nothing about a 0.8 mm rib, and a brochure rating belongs to the compound tested, not to another glass content of the same polymer. The listing itself appears in the compound's UL record, the Yellow Card. Why glass fibre changes burning behaviour is part of glass fiber reinforced plastics.

Glow wire, CTI, heat release and smoke: plastic ratings beyond UL 94#

Beyond UL 94, flame-retardant plastics are rated by 5 further tests: the glow wire (GWFI and GWIT), the comparative tracking index (CTI), the cone calorimeter (heat release), smoke density and, for cables, the EN 50399 bundle test with smoke and acidity classes. Household appliances show how a standard fixes the numbers: IEC 60335-1 clause 30.2.3 requires a GWFI of at least 850 °C and a GWIT of at least 775 °C for parts of unattended appliances carrying connections above 0.2 A, or a glow-wire test on the part at 750 °C with flaming of 2 s or less. Table 5 lists the 5 tests with the values this reference holds for flame-retardant plastics.

Footnote: Transport rules add FMVSS 302 (≤ 102 mm/min, 49 CFR 571.302), EN 45545-2 hazard levels (glass-filled PA66 R22 HL3, glass-filled PBT R22 HL2) and 14 CFR 25 Appendix F Part IV (2-minute heat release ≤ 65 kW·min/m2, peak ≤ 65 kW/m2).

The cone calorimeter, built by Babrauskas and colleagues at the US National Bureau of Standards (now NIST) in 1982, measures heat release by oxygen consumption, about 13.1 MJ per kg of oxygen consumed after Huggett. Bernhard Schartel (BAM) and T. R. Hull set out how to interpret cone calorimeter data for fire-retarded materials in Fire and Materials 31 (2007) 327-354, a paper with 1,462 citations in OpenAlex. Rail and vehicle parts follow the transport limits gathered under flame retardants for transportation.

What Does Flame Retardancy Cost a Plastic? 6 Property Trade-Offs#

Flame retardancy costs a plastic 6 properties: heat deflection temperature, tracking resistance, elongation and impact strength, surface appearance, hydrolysis resistance and colour freedom; in PC/ABS, for example, 20 wt% of an aryl phosphate lowers the heat deflection temperature to 72.6 °C. Table 6 lists the 6 trade-offs, where each one shows, the value this reference holds and the usual remedy.

Remedies follow the cause of each trade-off. Silane-, fatty-acid- or coupling-agent-treated ATH and MDH restore the elongation that raw mineral filler removes, which is why Huber's reference cable recipe carries 16 phr of coupling agents; coated grades are compared under mineral flame retardants (ATH and MDH). Phosphinate blends specified for a CTI of up to 600 V, such as Exolit OP 1312 in polyamide and OP 1240 in PBT, protect tracking resistance. Long-chain phase II APP (more than 1,000 units) resists water better than chains below 100 units, and red phosphorus and expandable graphite stay in dark parts. Heat deflection values are measured to ASTM D648 or ISO 75 at 0.455 or 1.82 MPa, so two grades compare only at the same load.

How Do You Specify a Flame-Retardant Plastic? 6 Steps#

Specify a flame-retardant plastic in 6 steps: name the fire standard and class, fix the thinnest wall and the colour, decide whether the grade must be halogen-free, check the processing temperature against the flame retardant, ask for test evidence at your thickness, and test the finished part. The 6 steps run from the requirement to the finished part, in the order below.

1. Name the fire standard and the class the part must meet: UL 94 V-0 at a thickness; IEC 60335-1 GWFI ≥ 850 °C and GWIT ≥ 775 °C for unattended appliances; an EN 45545-2 hazard level for rail; FMVSS 302 for car interiors; an EN 13501-6 class for cable. Standards are compared by application on the hub.
2. Fix the thinnest wall and the colour of the part, because a rating holds only at or above the rated thickness; the thinnest wall should sit at or above a rated thickness on the datasheet.
3. Decide whether the grade must use halogen-free flame retardants: cable acidity class a1 under EN 60754-2 rules out halogens, and the EU has barred halogenated flame retardants from the enclosures and stands of electronic displays since 1 March 2021 under Regulation (EU) 2019/2021. Halogen-free flame retardants for each polymer are compared by mechanism and loading.
4. Check the processing temperature against the flame retardant's onset: ATH and expandable graphite about 200 °C; phase II APP about 240 °C; zinc borate above 290 °C; AlPi and melamine cyanurate above about 300 °C; MDH about 320 °C. Engineering plastics process at about 240-320 °C.
5. Ask for the rating evidence at your thickness and colour: the UL listing, the technical data sheet, the safety data sheet and the test report. The listing system is explained under UL recognition and Yellow Cards for plastic compounds.
6. Test the finished part, for example with the end-product glow-wire test of IEC 60695-2-11 at 750 °C with flaming of 2 s or less, the alternative IEC 60335-1 accepts.

FR compound, FR masterbatch or in-house compounding?#

A flame-retardant plastic reaches the moulder in 3 forms: a ready FR compound that already carries its rating, an FR masterbatch that the converter lets down into natural resin, or flame-retardant additives that the converter or compounder blends in house; only the first arrives with a listed rating. The ready FR compound keeps its listed rating at its listed thickness and colour, because a UL 94 rating belongs to the compound that was tested. That makes the compound the lowest-risk route for a part that has to pass a defined class.

An FR masterbatch is a concentrate let down into natural resin at the moulding machine. FR-370 PP masterbatches of 25-80 % with a radical initiator are described in patents, the only FR masterbatch concentration in this reference. The let-down creates a new compound, so its rating should be confirmed by testing; let-down ratios are on flame retardant masterbatch.

In-house compounding blends the flame retardant itself into the polymer. Mineral routes put about 60 wt% of powder into the compound (160-180 phr), which needs a compounding line rather than a let-down at the press, as described under plastic compounding, and the result again needs its own fire test.

Which Rules Restrict the Flame Retardants Inside Plastic Parts?#

The rules on a flame-retardant plastic part follow the flame retardant inside it: RoHS caps PBDEs at 0.1 % per homogeneous material, Ecodesign Regulation (EU) 2019/2021 has banned halogenated flame retardants in display enclosures and stands since 1 March 2021, and any SVHC above 0.1 % w/w in an article triggers REACH Article 33 communication and a SCIP notification. Every ban and deadline is tracked under flame retardant regulations.

RoHS Directive 2011/65/EU, with Annex II as amended by Delegated Directive (EU) 2015/863, limits PBDEs to 0.1 % per homogeneous material in electrical and electronic equipment. Ecodesign Regulation (EU) 2019/2021 bans halogenated flame retardants in the enclosures and stands of electronic displays from 1 March 2021, a ban the EU General Court upheld.

US rules work substance by substance. TSCA section 6(h) prohibits distribution of most articles containing PIP (3:1) after 31 October 2026 (40 CFR 751.407), New York has banned organohalogen flame retardants in display enclosures and stands since 1 January 2024, and California AB 2998 has applied its 1,000 ppm limit to furniture and juvenile products since 1 January 2020.

Under REACH Article 33, any SVHC above 0.1 % w/w in an article triggers communication to recipients, an answer to consumer requests within 45 days and, since 5 January 2021, a SCIP notification. The Candidate List held 253 entries at its last update on 4 February 2026, and its flame-retardant entries are on the SVHC Candidate List. Table 7 lists 11 flame retardants found in plastic parts with their status.

Footnote: ATH, MDH, APP, AlPi, MPP, PAPP, expandable graphite, KSS and DOPO are not SVHCs (fact cards checked 22 Sep 2026).

DBDPE is an SVHC but not restricted. The European Commission mandated a REACH restriction of aromatic brominated flame retardants on 11 November 2025, a call for evidence ran from 21 January to 18 March 2026 and the draft Annex XV dossier is planned for December 2026, with non-polymeric substances in scope and polymeric ones out. Which brominated flame retardants fall under the planned restriction is listed by substance.

The PTFE anti-drip agent and PFBS-K fall within the proposed EU universal PFAS restriction: RAC adopted its final opinion on 2 March 2026, SEAC agreed a draft opinion on 10 March 2026 and expects its final opinion at the end of 2026, and nothing is in force. The PFAS restrictions page and the PTFE substance page track that dossier.

Who Supplies Flame-Retardant Plastics?#

Flame-retardant plastics come from 3 kinds of supplier: compounders that sell ready-rated FR grades, masterbatch makers that sell FR concentrates, and additive producers such as Clariant (Exolit), Huber (Martinal ATH and Magnifin MDH), Albemarle (Saytex), ICL, LANXESS, BASF (Melapur) and Adeka. The additive producers set what the compounders can achieve, and Table 8 lists 13 of them whose flame retardants go into flame-retardant plastics, with brands, chemistry and the plastics named in their product data.

Avient (formed as PolyOne in 2000, which added Clariant's masterbatch business in 2020) and Teknor Apex are compounders in this reference, without verified FR-grade data. Clariant announced an Exolit OP expansion at Daya Bay on 5 June 2026, and Huber completed its purchase of Martinswerk from Albemarle on 1 February 2016. The flame-retardant market is valued at USD 8.1-9.3 billion for 2025 across analyst estimates. Buyers should compare FR grades by the rating at their own thickness and colour, not by the letters FR in a grade name. Plants and certifications by company are in the directory of flame retardant manufacturers and suppliers.

─── The sections below cover related but broader questions, including safety, recycling and sheeting, that sit outside the core rating, specification and sourcing guidance above. ───

Are Flame-Retardant Plastics Safe to Use and to Recycle?#

Flame-retardant plastics are judged by the flame retardant they carry: the EU ENFIRO project, concluded in 2012, found good environmental and health profiles for APP, aluminium diethylphosphinate, ATH, MDH, MPP, DOPO and the zinc stannates, while TPP and melamine are now SVHCs. ENFIRO (EU Seventh Framework Programme, grant 226563) also found that RDP and BDP in styrenics gave more smoke, so a halogen-free label does not settle every question. Exposure studies for flame retardants are reviewed under flame retardants and human health.

Flame-retardant plastics in recycling#

Flame-retardant plastics complicate recycling when they carry legacy bromine: recycled material must hold less than 350 mg/kg of PBDEs from 30 December 2025 and 200 mg/kg from 30 December 2027, while a halogen-free PAPP and MPP package has reached UL 94 V-0 in recycled polypropylene. Those PBDE limits come from Delegated Regulation (EU) 2025/1482 under the EU POPs Regulation, which also sets 10 mg/kg for mixtures and articles and 10 mg/kg for toys and childcare articles made from recovered material from 17 May 2027. Sorting rules and legacy-additive limits are on how additives affect plastic recyclability.

Brominated polystyrene shows the other recycling route: its high molecular weight prevents blooming and limits bioavailability. High-molecular-weight polymeric flame retardants sit outside the planned ABFR restriction.

Fire-retardant plastic sheeting and film#

Fire-retardant plastic sheeting is thin polyethylene or polycarbonate film with a flame retardant compounded into it, sold for construction dust barriers and containment, and retailers rate it to tests such as NFPA 701 rather than to UL 94. NFPA 701, ASTM E84 and California Title 19 are the tests retailers cite for this film; their pass criteria are not covered in this reference, and sheeting is a retail product rather than a compound grade.

On the additive side, NOR HALS act as radical generators in thin film and give DIN 4102 B2 in transparent polyolefin films (Clariant), and FR-370 gives UL 94 V-2 in PP fibres. NOR HALS do this while also working as UV stabilizers, which suits film exposed outdoors; their UV role is covered under NOR HALS.

What is the most fire-resistant plastic?#

The most fire-resistant plastics are the inherently flame-resistant high-performance polymers PPS, PEEK, PEI and PSU, and among the plastics with a sourced limiting oxygen index in this reference, polycarbonate is highest at 25-29 vol % O2. This reference does not rank PPS, PEEK, PEI and PSU against each other, because it holds no grade-level LOI or UL 94 value for them. Building materials such as mineral wool or gypsum fall outside plastics.

Is PVC flame retardant?#

Yes, PVC is inherently flame retardant because the polymer is 57 % chlorine by mass, but flexible PVC still needs ATH and zinc borate to reach a limiting oxygen index of 26-27 vol % O2 and UL 94 V-0 at 3 mm, and it releases hydrogen chloride when it burns. That hydrogen chloride keeps PVC out of acidity class a1 cables. Smoke suppressants are compared on flame retardants and smoke suppressants for PVC.

Are flame-retardant plastics toxic?#

Flame-retardant plastics are not toxic as a class; the concern sits with specific flame retardants, such as antimony trioxide (harmonised Carc. 2), TBBPA (Carc. 1B since 1 September 2025) and the SVHCs TPP and melamine, while ATH, MDH and phosphinates carry no SVHC listing. The wider question is plastic toxic is answered polymer by polymer, by additive content.

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Every figure on this page is checked against primary sources; see our sourcing standards and fact-checking process.

Byline: PlasticAdditives.net Editorial Team

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