Flame Retardancy Performance Testing of New Materials: Standards, Methods, and Applications

Flame retardancy performance testing evaluates how new and advanced materials ignite, propagate flame, release heat, and generate smoke under standardized fire conditions. By applying internationally recognized methods such as limiting oxygen index (ISO 4589-2), UL 94 burning tests (IEC 60695-11-10), glow-wire testing (IEC 60695-2 series), and cone calorimetry (ISO 5660-1), manufacturers can verify fire safety, demonstrate regulatory compliance, and accelerate market entry. This guide summarizes the sample types, testing items, testing methods, and industry applications relevant to flame retardancy testing of new materials at accredited third-party laboratories.

Technical Overview

Flame retardancy performance testing is a systematic evaluation of how a material behaves when exposed to an ignition source, heat flux, or simulated fault condition. The core parameters assessed include ignitability, burning rate, flame propagation, heat release, smoke production, combustion gas toxicity, and the formation of flaming droplets or particles. For new and advanced materials—such as flame-retardant polymer compounds, fiber-reinforced composites, nanocomposites, bio-based polymers, aerogel insulation, and battery components—quantitative fire performance data is essential for material selection, product certification, and liability management.

Testing is performed according to standards published by ISO, IEC, ASTM, EN, UL, JIS, and GB standardization bodies. Because fire behavior depends strongly on geometry, thickness, and end-use conditions, laboratory programs typically combine small-scale screening tests (for example, limiting oxygen index and UL 94) with intermediate-scale heat release and smoke tests (for example, cone calorimetry and smoke density chambers). Accredited third-party laboratories provide ISO/IEC 17025-controlled test conditions, traceable calibration, and reports that are accepted by regulators, certification bodies, and OEM supply chains worldwide.

• Ignitability and ease of ignition under small flame, glow-wire, or radiant exposure
• Flame spread and self-extinguishing behavior after removal of the ignition source
• Heat release rate, total heat release, and effective heat of combustion
• Smoke opacity, smoke toxicity, and corrosive gas evolution
• Flaming drips and secondary ignition risk, which are critical for electronic enclosures

Testing Samples

Engineering Thermoplastics and Thermosets

Test specimens include injection-molded bars and plaques of polycarbonate (PC), polyamide (PA66, PA6), polyester (PBT, PET), polyphenylene sulfide (PPS), polyetherimide (PEI), ABS, PP, and epoxy or phenolic thermosets, in both unfilled and flame-retarded grades (halogenated, phosphorus-based, nitrogen-based, mineral-filled, or intumescent systems).

Composites and High-Performance Fiber Materials

Carbon-fiber and glass-fiber laminates, sheet molding compounds (SMC/BMC), aramid fabrics, ceramic-fiber boards, and hybrid nanocomposite panels are tested to qualify materials for rail, aerospace, and structural applications where flame spread and smoke limits are stringent.

Foams and Thermal Insulation Materials

Rigid and flexible polyurethane foams, polyolefin foams, EPS/XPS boards, phenolic foams, rock wool, and aerogel blankets are evaluated for horizontal burning behavior, flame spread, and smoke production relevant to insulation and cushioning applications.

Films, Coatings, Adhesives, and Sealants

Thin substrates require adapted specimen preparation: films are typically wrapped on mandrels or laminated to defined carriers, while intumescent coatings are applied at specified thicknesses to standard substrates before testing.

Electrical, Electronic, and Energy Storage Materials

Samples include PCB laminates (FR-4 and halogen-free grades), potting and encapsulation compounds, connector housings, battery module covers, mica-based thermal barriers, separator coatings, and structural components for lithium-ion battery packs and charging infrastructure.

Textiles and Flexible Materials

Upholstery fabrics, protective clothing textiles, nonwovens, and membranes are tested for limited flame spread and afterflame behavior using small- and full-scale flame sources appropriate to the end use.

Testing Items

A typical flame retardancy test program for a new material combines the following items, selected according to the target application and regulatory framework:

• Limiting oxygen index (LOI) — ISO 4589-2 / ASTM D2863 / GB/T 2406.2 / JIS K 7201-2
• Horizontal and vertical burning (UL 94 HB, V-0, V-1, V-2, 5VA, 5VB) — IEC 60695-11-10, IEC 60695-11-20, GB/T 2408, GB/T 5169.16
• Glow-wire flammability index (GWFI) — IEC 60695-2-12 / GB/T 5169.12
• Glow-wire ignition temperature (GWIT) — IEC 60695-2-13 / GB/T 5169.13
• Needle-flame test — IEC 60695-2-2 / GB/T 5169.5
• Heat release rate, peak heat release rate, and total heat release (cone calorimeter) — ISO 5660-1 / ASTM E1354
• Mass loss rate and effective heat of combustion
• Smoke production rate and specific optical density — ISO 5659-2 / ASTM E662
• Toxic and corrosive fire effluent analysis (CO, CO2, HCN, HCl, HF, SO2, NOx) — EN 17077 / ISO/TS 19700
• Single-flame-source ignitability and flame spread — EN ISO 11925-2 / ISO 15025
• Single burning item (SBI) test and Euroclass classification inputs — EN 13823 / EN 13501-1
• Non-combustibility and gross heat of combustion — EN ISO 1182 / EN ISO 1716
• Surface burning characteristics (Steiner tunnel) — ASTM E84
• Microscale combustion calorimetry (MCC) for R&D screening — ASTM D7309
• Automotive interior horizontal burn — ISO 3795 / GB 8410
• Railway fire safety requirement sets — EN 45545-2
• Flame propagation on cables — IEC 60332-1-2 and IEC 60332-3 series

Testing Methods

Limiting Oxygen Index (ISO 4589-2 / ASTM D2863)

A vertical specimen is ignited at its top edge in a glass chimney with a controlled mixture of oxygen and nitrogen. The LOI is the minimum oxygen concentration, expressed in volume percent, at which the specimen sustains burning for a defined time or length. Since ambient air contains approximately 21% oxygen, materials with an LOI below 21 burn readily in air, LOI values of 27 and above are generally considered self-extinguishing, and values above 32 indicate strong flame retardancy. Specimens are typically 80–150 mm long by 10 mm wide with thicknesses from 3 mm to 10 mm depending on the specimen type, and several specimens are tested at different oxygen concentrations to bracket the critical value.

UL 94 Vertical and Horizontal Burning (IEC 60695-11-10 / GB/T 2408)

The UL 94 vertical (V) test applies a 50 W (20 mm) methane flame for 10 seconds to the bottom of a vertically clamped bar (125 mm × 13 mm at the relevant thickness), twice per specimen, with dry surgical cotton placed beneath. Two sets of five conditioned specimens are tested. The classification criteria are:

• V-0: afterflame time of each specimen does not exceed 10 seconds; total afterflame time for each set does not exceed 50 seconds; no flaming drips igniting the cotton
• V-1: afterflame time does not exceed 30 seconds; total for each set does not exceed 250 seconds; no flaming drips igniting the cotton
• V-2: same timing criteria as V-1, but flaming drips are permitted provided secondary ignition is limited according to the standard

The horizontal (HB) test measures burning rate along a horizontal bar; ratings require a burning rate not exceeding 75 mm/min for thicknesses below 3 mm and 40 mm/min for thicknesses of 3 to 13 mm, or extinguishing before the 100 mm mark. The more severe 5VA/5VB tests apply a 500 W (125 mm) flame five times to both bars and plaques; 5VA (the highest UL 94 rating) requires no burn-through hole in the plaque. Because ratings are thickness-specific, materials should be tested at both minimum and maximum production wall thickness.

Glow-Wire Testing (IEC 60695-2-11/-12/-13)

Glow-wire tests simulate thermal stress from overheated or glowing components in fault conditions. A temperature-controlled glow wire (550 °C to 960 °C) is pressed against the specimen for 30 seconds. GWFI is the highest temperature at which the specimen does not ignite or self-extinguishes within 30 seconds without igniting the wrapping tissue below. GWIT is derived from the highest glow-wire temperature at which no ignition occurs during the specified contact, expressed with a defined safety margin above the measured ignition temperature. Product safety standards such as IEC 60335-1 commonly require GWIT of 750 °C for parts supporting live connections and GWFI of 850 °C for surrounding parts.

Needle-Flame Test (IEC 60695-2-2)

A small 12 mm flame is applied to the specimen for defined durations to simulate small fault arcs. The specimen passes if flame or afterglow extinguishes within 30 seconds, the wrapping tissue is not ignited, and the underlying pine board is not burned through.

Cone Calorimetry (ISO 5660-1 / ASTM E1354)

A 100 mm × 100 mm specimen is exposed to a radiant heater at a chosen irradiance (commonly 25, 35, or 50 kW/m²) with or without piloted ignition. Using the oxygen consumption principle, the test delivers the most complete bench-scale fire profile: time to ignition, heat release rate (HRR), peak HRR, total heat release (THR), effective heat of combustion, mass loss rate, smoke production rate, and yields of CO and CO2. Cone data are widely used for R&D benchmarking of flame-retardant formulations and as input for fire modeling.

Smoke Density and Effluent Toxicity (ISO 5659-2 / EN 17077)

Specimens are exposed in a closed chamber to a radiant source (typically 25 kW/m²) with and without a pilot flame, and light transmittance is recorded to calculate specific optical density (Ds max and VOF4). Coupled FTIR gas analysis quantifies toxic species, which feed into toxicity indices such as CITLP required by EN 45545-2 for railway applications.

Building Product Reaction-to-Fire Tests (EN 13501-1 / ASTM E84 / GB 8624)

Construction materials are classified through combined test batteries: EN ISO 11925-2 (single flame source) for classes E and B, EN 13823 (SBI) for classes B through D, and EN ISO 1182 and EN ISO 1716 for classes A1 and A2. In North America, the ASTM E84 Steiner tunnel determines flame spread and smoke developed indices for Class A, B, or C ratings. The Chinese GB 8624 classification (A, B1, B2, B3) is based on the corresponding GB/T test methods.

Screening with Microscale Combustion Calorimetry (ASTM D7309)

Milligram-scale samples are pyrolyzed at a controlled heating rate and the decomposition products are combusted to determine heat release capacity, peak HRR per unit mass, and total heat of combustion. MCC requires minimal material, making it ideal for early-stage screening of new formulations before full-scale qualification.

Applications

Flame retardancy test data underpins regulatory compliance and design verification across all major sectors that adopt new materials:

• Consumer electronics and IT equipment: enclosures, chargers, connectors, and relays qualified to UL 94 V-0 and IEC 60950-1/IEC 62368-1 fire requirements
• Wire and cable: insulation, sheathing, and halogen-free (LSZH) compounds evaluated under IEC 60332 and EN 50575 requirements
• New energy and e-mobility: battery module housings, busbar insulation, thermal barriers, and high-voltage connectors supporting GB 38031 and related EV safety standards
• Photovoltaics and charging infrastructure: junction boxes, backsheets, and switchgear components requiring GWFI 960 °C performance
• Home appliances: insulating parts verified by GWIT and GWFI testing under IEC 60335-1
• Rail and aerospace interiors: composites, seat materials, and panels meeting EN 45545-2 hazard sets and aircraft interior flammability regulations
• Construction: insulation boards, curtain wall cores, flooring, and coatings classified under EN 13501-1, ASTM E84, and GB 8624
• Furniture and textiles: upholstered seating and protective fabrics verified for limited flame spread
• Materials R&D: halogen-free formulation development benchmarked by LOI, UL 94, MCC, and cone calorimetry

FAQ

What LOI value indicates that a material is flame retardant?

Because air contains about 21% oxygen, materials with an LOI below 21 will typically continue burning in air once ignited. In engineering practice, LOI values of 27 to 28 and above are generally regarded as self-extinguishing, while values above 32 indicate high flame retardancy. LOI is best used for formulation comparison rather than as a standalone compliance criterion.

What is the difference between UL 94 V-0, V-1, and V-2?

All three are vertical burning ratings based on afterflame time, total afterflame time, and dripping behavior. V-0 requires the shortest afterflame times (10 seconds per ignition, 50 seconds total per set), V-1 allows up to 30 seconds per ignition and 250 seconds total, and V-2 matches the V-1 timing but tolerates flaming drips under defined conditions. V-0 is the most common specification for electronic enclosures.

How do GWFI and GWIT differ?

GWFI (IEC 60695-2-12) evaluates whether a material ignites or drips when contacted by a hot glow wire and whether burning self-extinguishes, expressed as the highest passing temperature. GWIT (IEC 60695-2-13) identifies the glow-wire temperature at which the material does not ignite during the 30-second contact, reported with a defined safety margin. GWFI addresses flame and dripping behavior; GWIT addresses ignition sensitivity.

Why must flame ratings be reported with a thickness?

Fire performance is strongly geometry-dependent. A compound rated V-0 at 3.0 mm may only achieve V-2 or fail at 1.0 mm. Ratings are only valid for the thickness tested, so certification programs should always include the minimum production wall thickness.

How many specimens are required and what conditioning is applied?

Typical requirements are two sets of five bars for UL 94 V testing at each thickness, five to fifteen specimens for LOI, three specimens per temperature for glow-wire tests, and a minimum of three specimens for cone calorimetry. Specimens are conditioned at 23 ± 2 °C and 50 ± 5% relative humidity for at least 48 hours before testing.

Are GB, IEC, and UL standards interchangeable?

Many GB standards, such as GB/T 2408 and the GB/T 5169 series, are technically aligned or modified adoptions of the corresponding IEC 60695 methods, so results are usually comparable. However, certification schemes, marking, and factory surveillance requirements differ between systems, so the target market should be confirmed before testing begins.

How long does flame retardancy testing take?

Standard small-scale tests such as LOI, UL 94, glow-wire, and needle-flame typically require 5 to 10 working days after specimen conditioning. Cone calorimetry, smoke toxicity analysis, and full building-product classification programs involve longer chains of tests and may require several weeks. Accredited third-party laboratories can consolidate multiple methods into a single program to shorten the overall schedule.

Can novel materials without an applicable standard be tested?

Yes. Nanocomposites, aerogels, bio-based polymers, and additively manufactured parts are usually assessed by analogy: existing bench-scale methods (LOI, UL 94, MCC, cone calorimeter) are applied to representative specimens, and deviation notes document any adaptations such as specimen mounting or substrate selection. The resulting data support risk assessment while formal standardization catches up with the material technology.