XPS Board Fire Rating: Flame Retardants, Euroclass E and NFPA 285

XPS board fire rating is not one number. Unfaced XPS is typically Euroclass E under EN 13501-1, China grades it B1 or B2 under GB 8624, and US data sheets report ASTM E84 surface-burning values, while NFPA 285 tests the whole wall rather than the board. All these results depend on an HBCD-free flame retardant, correctly dosed, and on the end use.

For a producer, this is a formulation, plant-control and market-access question at the same time. This article explains what each rating measures, how the flame retardant changed after HBCD, and what your line and laboratory have to do. How the board is formed is covered in our XPS manufacturing process guide.

Why the XPS Board Fire Rating Depends on the Test

The same board can carry several ratings, because each system asks a different question. Reaction-to-fire tests ask how a material behaves when ignited. Assembly tests ask whether a wall spreads fire. Fire-resistance tests, such as ASTM E119, ask how long an assembly holds back a fire, and a foam board has no such rating on its own.

Do not treat these as equal. Never tell a buyer that one rating “equals” another unless the governing standard says so, and always ask which test the project specification actually names.

Euroclass E Under EN 13501-1

Euroclass E is the rating most buyers mean when they ask for the European XPS foam board fire rating. Under the EU classification table (Commission Delegated Regulation (EU) 2016/364), a Class E product is tested to EN ISO 11925-2 with a 15-second flame exposure, and flame spread must not exceed 150 mm within 20 seconds. Flaming droplets are also assessed.

Classes B, C and D use a longer 30-second exposure with a 60-second limit, and also require the larger single burning item test (EN 13823). Class F is what remains when a product does not reach Class E.

Three practical points:

• E is a small-flame result. It shows that the product resists ignition by a small flame, not that it is non-combustible. Sales materials should not imply more.
• Class E is what unfaced XPS normally declares. Our EN 13164 guide explains how the class is declared in a CE Declaration of Performance, along with the verification system that typically applies.
• Class E needs flame retardant. Unretarded polystyrene foam generally will not pass. When BASF moved its European range away from HBCD, it reported that the replacement still allowed insulation that meets Class E (Global Insulation, 2014).

China’s B1 and B2 Grades for XPS

Many buyers in Asia, the Middle East and Africa ask for “B1” because Chinese suppliers quote it. GB 8624-2012, still in force until its replacement takes effect, sets out grades A (non-combustible), B1 (flame retardant), B2 (combustible) and B3 (flammable), and its introduction says it draws on the European system. China’s XPS product standard, GB/T 10801.2-2018, tests combustion performance according to GB 8624 and uses Grade B2 as its labeling example.

Its replacement, GB 8624-2025, was issued on 31 December 2025 and takes effect on 1 January 2027. It treats insulation as a separate class of product. We have read the approval draft that China’s fire authority published in September 2025, not the final text, so the table below shows the draft’s wall insulation criteria. Check every value against the published standard before you rely on it:

For roof and floor insulation, the draft sets a lower B1 oxygen index of 26.0%. It also states that the oxygen index is necessary but cannot alone decide the grade. That is an important warning for plants, because oxygen index is the easy test to run in-house. A pass does not establish a B1 grade.

B1 does not mean that a board will not burn. A 2025 cone-calorimeter study in the journal Fire tested XPS graded B1 and B2 under GB 8624-2012. Peak heat release rose with heat flux for both, reaching 535 kW/m² for B1 and 579 kW/m² for B2 at 55 kW/m². Critical heat flux was close, at 19.28 and 20.88 kW/m², and the authors concluded the flame retardant level had limited influence on that value. Both of those boards used HBCD, so the numbers are not a guide to a new formula. The principle holds: a grade describes a test result, not immunity from fire.

ASTM E84 Values for XPS

US rules work on surface-burning indices. Under Chapter 26 of the 2018 International Building Code, foam plastic insulation must have a flame spread index of 25 or less and a smoke-developed index of 450 or less, tested to ASTM E84 or UL 723.

For reference, Owens Corning’s October 2025 data sheet for FOAMULAR NGX 250 lists flame spread 10 and smoke developed 175. The same sheet says plainly that “This product is combustible” and that a protective or thermal barrier is required as specified in the building code. It also warns that these laboratory tests do not describe the hazards under actual fire conditions, and gives a maximum service temperature of 74 °C. That is a sensible model for your own literature. For how ASTM’s XPS grades are organized, see ASTM C578 types.

XPS Insulation and NFPA 285

NFPA 285 is the search term that causes the most confusion, because it is “an assembly and not a material test” (The Construction Specifier). No board can be NFPA 285 rated on its own. What can be said is that a specific wall assembly, using a specific XPS product, passed.

The requirement comes from IBC Section 2603.5.5: exterior walls of any height on Type I–IV construction containing foam plastic insulation must be tested to NFPA 285 and meet its acceptance criteria. An ICC summary adds that the foam must also meet the E84 limits and be separated from the interior by a thermal barrier. Owens Corning publishes wall assemblies with FOAMULAR XPS continuous insulation that have passed NFPA 285, with masonry veneer over steel stud or masonry back-up walls, which shows the result is tied to a defined build-up of layers.

For a new producer, this has real consequences:

• A pass belongs to the tested assembly. Changing the facing, air barrier or cladding can take a wall outside what was tested.
• Your board is a component. You may need a façade system owner to include your product in their test program, or you may need to fund a test yourself.
• Formula changes matter. If a test report relies on your flame retardant formula and density, tell the system owner before you change them.

NFPA 285 in the Gulf

This matters beyond North America. A Gulf technical review says that Saudi codes SBC 201 and SBC 801 are largely based on the IBC and IFC, and that SBC assesses fire propagation under NFPA 285. The UAE’s Fire and Life Safety Code uses facade assembly testing to NFPA 285 or BS 8414 in its approach to fire stopping, and Gulf News reported in 2018 that it specified non-combustible insulation in cladding systems.

So check before you plan around facade sales. In parts of the Gulf, XPS may be far easier to sell for roofs, floors, foundations and cold storage than for high-rise external walls. Confirm the current rule with the local civil defense authority or a fire consultant in each market, because these codes change.

The HBCD Phase-Out

For decades, hexabromocyclododecane (HBCD) was the standard flame retardant in XPS. It no longer belongs in a new formula.

The Stockholm Convention’s Conference of the Parties listed HBCD in Annex A through decision SC-6/13 in 2013, with specific exemptions for production and for use in expanded and extruded polystyrene in buildings. The depositary communicated the amendment on 26 November 2013. Under the amendment, those using the exemption had to make sure that foam containing HBCD could be identified throughout its life cycle, by labeling or other means.

The exemptions were time-limited. These entries appear on the Convention’s register:

Every entry for buildings has expired. In practice, an investor should plan an HBCD-free line from the first trial. Some Parties accept Convention amendments under a separate procedure, so check national law as well as the register, especially for a country that is not listed here. Importers and project specifiers increasingly ask for written evidence too.

Flame Retardants That Replace HBCD

The Convention’s BAT/BEP guidance on HBCD (March 2021) gives useful baselines. XPS panels could contain 0.8–2.5% w/w HBCD, and an XPS masterbatch about 40% w/w. It also reviews alternatives:

The guidance also warns that alternatives may have a broad range of environmental impacts and need case-by-case assessment. It does not provide a universal dosage for polymeric flame retardants, and neither should a supplier without testing your formula. Polystyrene grade, density, thickness, blowing agent and nucleating agent all affect the outcome. Rules also differ between markets and keep changing, so ask each flame retardant supplier for a current safety data sheet and regulatory statement for your destination countries.

BASF’s PolyFR switch shows that the industry moved early in Europe. The company changed its Styropor, Neopor and Styrodur ranges nine months ahead of the EU’s REACH deadline of 21 August 2015 (Global Insulation, 2014). Your local market may be behind that, but export customers usually are not.

What the Fire Rating Means for Your XPS Line

The fire rating is earned at the feeder and the extruder, not in the certificate. In practical terms:

1. Dose by weight and log it. Flame retardant is a small stream, so use gravimetric feeding, with feed-rate records tied to batch numbers. A drift below target can fail a fire test while the board still looks fine.
2. Disperse it fully. Poor mixing leaves local weak spots. This is one reason a twin-screw first stage is the standard on high-output tandem lines: better mixing and a wider choice of formulations. Single-screw tandems are an economical option, but confirm dispersion for the flame retardant you intend to use. See XPS extruder for the comparison.
3. Balance the recycling loop. The BAT/BEP guidance says trim can reach about 15–25% of feed material. Recycled trim already contains flame retardant and has already had a heat history, so keep the ratio steady and test at your normal recycled level, not on virgin-only trial boards.
4. Be careful with outside recycled polystyrene. Old foam may contain HBCD. Test it against your specification and your market’s limit on HBCD content before using it, and check the screening requirements under the Basel Convention guidelines for waste foam.
5. Fix the blowing agent first. On the lines we supply, CO₂ with alcohol as a co-blowing agent is the standard. Alcohol and hydrocarbon co-blowing agents are flammable, so fire-test boards from your actual formula after their normal storage period. See our XPS blowing agents guide.
6. Test across the range. Boards on our reference lines usually run 20–60 mm thick at 30–45 kg/m³. Check the field of application in each classification report, and plan tests to cover the thickness and density limits you will sell.
7. Run factory checks, and leave certification to a laboratory. Oxygen index and small-flame ignition tests are useful routine controls. Classification still has to come from the lab and procedure your market recognizes. Keep retained samples from each batch.

If your market is comparing insulation types, our XPS vs EPS article explains how the two foams differ as products and in the choice of line.

FAQ

What is the fire rating of XPS foam board?

The XPS foam board fire rating depends on the test. Unfaced XPS is typically Euroclass E under EN 13501-1. In China, boards are graded B1 or B2 under GB 8624. US data sheets report ASTM E84 values, such as flame spread 10 and smoke developed 175 on one current product. Ask which test your project specifies, since these ratings are not interchangeable.

Is XPS insulation combustible?

Yes. XPS is a polystyrene foam, and flame retardant slows ignition and flame spread under test conditions without making it non-combustible. One major US producer states on its data sheet that its product “is combustible” and needs a protective or thermal barrier as specified in the building code. Producers should say the same in their own technical literature.

Does XPS insulation pass NFPA 285?

NFPA 285 tests a wall assembly, not a board, so XPS insulation cannot pass on its own. Published wall systems using XPS continuous insulation have passed in specific build-ups, such as masonry veneer over steel stud or masonry back-up walls. A pass only covers the assembly tested, so any new XPS product has to be tested in, or evaluated for, that wall system.

Is HBCD banned in XPS?

HBCD was listed in Annex A of the Stockholm Convention in 2013, with exemptions for EPS and XPS in buildings. All of the exemptions for buildings on the Convention’s register have now expired, including those of the European Union, Saudi Arabia, Türkiye and China. Confirm the position in national law for your market, and build any new plant’s formula around an HBCD-free flame retardant.

Is China B1 the same as Euroclass E?

No. In the approval draft of GB 8624-2025, the small-flame E test falls under B2 (E), while B1 requires the larger single burning item test and a 30-second ignition test, along with a higher oxygen index for wall insulation. Check the published standard and the actual test report. A supplier’s “B1” label is not evidence of a European class.

Planning an XPS Plant Around Your Fire Rating?

The fire classification your market requires should shape the flame retardant dosing, mixing and recycling arrangement from the start. See our XPS foam board production line for the equipment, and the XPS board plant setup guide for the full planning sequence.

Sources

• European Commission, Commission Delegated Regulation (EU) 2016/364 on the classification of the reaction-to-fire performance of construction products (text mirror): https://lawplayer.com/eu/act/32016R0364
• GB 8624-2012, Classification for burning behavior of building materials and products (standard listing): https://www.chinesestandard.net/PDF-EN/GB8624-2012EN-P15P-H12580H-777937.pdf
• GB 8624-2025, Classification for burning behavior of building materials and products (standard listing): https://www.chinesestandard.net/PDF/PDF.amp.aspx/GB8624-2025
• China Fire and Rescue, GB 8624-202X approval draft, published for comment September 2025: https://www.119.gov.cn/site1/images/zfxxgk/fdzdgknr/zqyj/2025/09/30/1759220204687062654.pdf
• GB/T 10801.2-2018, Rigid extruded polystyrene foam boards for thermal insulation (standard listing): https://www.chinesestandard.net/PDF/GDOC.aspx/GBT10801.2-2018
• Improving Combustion Analysis of Extruded Polystyrene via Custom Isolation Methodology, Fire, 2025: https://www.mdpi.com/2571-6255/8/2/43
• Owens Corning, FOAMULAR NGX 250 XPS Insulation Product Data Sheet, Pub. No. 43522-V, October 2025: https://www.owenscorning.com/dms/43522
• International Code Council, Foam Plastic Insulation: Exterior Wall Fire Safety: https://www.iccsafe.org/wp-content/uploads/Foam-Plastic-Insulation-–-Exterior-Wall-Fire-Safety-.pdf
• The Construction Specifier, Continuous insulation performance: https://www.constructionspecifier.com/continuous-insulation-performance/2/
• Owens Corning, Commercial Complete Wall System (catalog): https://pdf.archiexpo.com/pdf/owens-corning-insulation/commercial-complete-wall-system/62416-74383.html
• A. Faza, GCC Codes Facade Fire: Key Methodologies, WFM Media, 2022: https://wfmmedia.com/gcc-codes-facade-fire-key-methodogies/
• Gulf News, Strict new tests to ensure fire safety in towers, 2018: https://gulfnews.com/uae/strict-new-tests-to-ensure-fire-safety-in-towers-1.2024716
• United Nations, Depositary Notification C.N.934.2013, Stockholm Convention amendment listing HBCD (decision SC-6/13): https://treaties.un.org/doc/Publication/CN/2013/CN.934.2013-Eng.pdf
• Stockholm Convention, Hexabromocyclododecane (HBCD) overview: https://www.pops.int/Implementation/IndustrialPOPs/HBCD/Overview/tabid/7410/Default.aspx
• Stockholm Convention, Register of specific exemptions for HBCD: https://chm.pops.int/Implementation/Exemptions/SpecificExemptions/HexabromocyclododecaneRoSE/tabid/5034/Default.aspx
• Stockholm Convention, BAT/BEP Guidance for the use of HBCD, March 2021: https://nips.pops.int/Guidance_docs/Document_2_4_4.pdf
• Global Insulation, European EPS and XPS portfolio switched to PolyFR ahead of REACH deadline, December 2014: https://globalinsulation.com/news/954-european-eps-and-xps-portfolio-switched-to-polyfr-ahead-of-reach-deadline