Synthetic Leather Afterflame Time Testing: Standards, Methods, and Technical Requirements

Synthetic leather afterflame time testing measures how long a PU, PVC, or microfiber leather specimen continues to burn with visible flame after the ignition source is removed, making it one of the most critical indicators of flame-retardant performance. This technical article explains the test principle, applicable standards such as GB/T 5455, GB/T 2408, UL 94, and ISO 6941, specimen preparation requirements, measurement procedures, acceptance criteria, and typical applications across automotive, furniture, rail, and aviation industries.

Technical Overview

Synthetic leather—including polyurethane (PU), semi-PU, polyvinyl chloride (PVC), and microfiber variants—is a polymer-coated or polymer-impregnated textile material widely used in seating, automotive interiors, furniture, footwear, and wall coverings. Because the polymer layers and textile backing are combustible and thermoplastic materials may melt and drip during burning, flammability performance is a mandatory safety attribute for most end uses. The afterflame time test is the core measurement used to quantify how quickly a material stops burning once the external flame is withdrawn.

Afterflame time is defined as the duration, in seconds, during which a specimen continues to flame after the defined ignition source has been removed. It is distinguished from afterglow time, which measures flameless glowing combustion that may continue after the visible flame extinguishes. Together with damaged (char) length, flaming drip behavior, and flame spread rate, these parameters form the basis of flammability classification for coated fabrics and flexible polymeric materials.

The most widely applied test frameworks include GB/T 5455 (vertical flame test for textile fabrics, measuring afterflame time, afterglow time, and damaged length), GB/T 2408 together with IEC 60695-11-10 and UL 94 (horizontal and vertical burning of plastics with V-0/V-1/V-2 classification), ASTM D6413 (vertical flame resistance of textiles), ISO 6940 and ISO 6941 (ignition ease and flame spread of vertically oriented fabrics), and ISO 15025 (flame spread test methods for protective clothing materials). Regulatory burn tests such as GB 8410, ISO 3795, and FMVSS 302 for vehicle interiors, and FAR 25.853 for aircraft cabin materials, impose explicit afterflame time limits. Accredited third-party laboratories routinely perform these tests to support regulatory compliance, product certification, incoming quality control, and flame-retardant formulation development.

Testing Samples

Polyurethane (PU) and Semi-PU Synthetic Leather

PU synthetic leather consists of a woven or knitted fabric substrate coated with one or more polyurethane layers, often with a surface finish. PU materials tend to soften and melt when exposed to flame, so afterflame time, melt-drip behavior, and afterglow are all recorded. Specimens are prepared in both machine and cross directions because the textile substrate orientation can influence flame propagation.

Polyvinyl Chloride (PVC) Synthetic Leather

PVC synthetic leather combines a textile backing with plastisol coating layers containing plasticizers and fillers. Plasticizer content significantly affects ignitability and burning duration, and chlorine in the polymer matrix can influence self-extinguishing behavior. PVC specimens are tested for afterflame time, afterglow, char length, and whether flaming droplets are produced.

Microfiber Synthetic Leather

Microfiber (ultra-fine fiber) synthetic leather uses a three-dimensional fiber structure impregnated with polyurethane elastomer. Its relatively high polymer loading and dense fiber network can produce different burning behavior than conventional coated fabrics, so dedicated afterflame time verification is required for automotive, furniture, and apparel applications.

Specimen Preparation and Conditioning

Specimen dimensions and quantities depend on the applicable standard:

• GB/T 5455 and ASTM D6413 vertical flame test: rectangular specimens of 300 mm × 80 mm (or 300 mm × 76 mm), typically five specimens in the length direction and five in the width direction.
• GB/T 2408 / IEC 60695-11-10 / UL 94 vertical test: bar specimens of 125 mm × 13 mm, normally five specimens per set; thin flexible materials may require rolled specimens under the thin-material vertical (VTM) procedure.
• GB 8410 / ISO 3795 / FMVSS 302 horizontal vehicle-interior test: specimens of 356 mm × 102 mm with thickness as supplied, up to the maximum permitted thickness.
• Specimens must be free of creases and surface contamination, and decorative finishes, adhesives, or laminated layers must be tested in the final construction as used in service.

Unless otherwise specified, specimens are conditioned in a standard atmosphere of 20 ± 2 °C and 65 ± 4 % relative humidity (per GB/T 6529 / ISO 139) for at least 24 hours before testing. Certain standards also permit or require oven drying followed by cooling in a desiccator to evaluate behavior in a dry state.

Testing Items

The afterflame time test program for synthetic leather typically covers the following measurable parameters:

• Afterflame time (s): duration of visible flaming after removal of the ignition source, recorded for each specimen and averaged across the set.
• Afterglow time (s): duration of glowing combustion without flame following flameout.
• Damaged length / char length (mm): extent of material destruction along the specimen, often determined by marker-thread methods in vertical fabric tests.
• Flaming drips and debris: whether molten droplets fall and whether they ignite an indicator medium placed below the specimen.
• Ignition ease and flame spread rate: complementary metrics obtained from ISO 6940/6941 or horizontal vehicle-interior tests (expressed in mm/min).
• Complementary flammability indices: limiting oxygen index (LOI) per GB/T 2406.2 / ISO 4589-2 is frequently tested alongside afterflame time to characterize intrinsic flame retardancy.

Testing Methods

Vertical Flame Method (GB/T 5455 / ASTM D6413 / ISO 6941)

In the vertical fabric method, the specimen is suspended vertically in an enclosed test cabinet with its lower edge exposed to a calibrated gas burner flame (typically 40 ± 2 mm in height for GB/T 5455). The flame is applied to the lower edge for a defined ignition period, commonly 12 seconds, after which the burner is removed. Using a stopwatch or automatic timing device with 0.1 s resolution, the operator records the afterflame time from the moment of flame removal until visible flaming ceases, followed by the afterglow time until glowing stops. Marker threads and weights may be used to determine damaged length. Results are reported as individual values, averages, and the maximum observed value for each specimen direction.

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

When synthetic leather or its coating layers are evaluated as polymeric materials, bar specimens are subjected to the plastics burning test. In the vertical configuration, a 20 mm blue flame is applied to the lower end of the specimen for 10 seconds; the first afterflame time (t1) is recorded. After the flame extinguishes, the burner is reapplied for another 10 seconds to record the second afterflame time (t2), afterglow time, and any flaming drips. The horizontal configuration (HB classification) measures linear burning rate instead. The classification criteria for the vertical test are:

• V-0: individual afterflame time not exceeding 10 s; total afterflame time for all specimens not exceeding 50 s; no flaming drips that ignite cotton.
• V-1: individual afterflame time not exceeding 30 s; total afterflame time not exceeding 250 s; no flaming drips that ignite cotton.
• V-2: timing criteria identical to V-1, but flaming drips that ignite cotton are permitted.

Regulatory Burn Tests for Vehicles, Aircraft, and Furniture

For automotive interior applications, GB 8410, ISO 3795, and FMVSS 302 specify a horizontal burning test in which the material must either self-extinguish or burn at a rate not exceeding 100 mm/min; afterflame behavior directly determines whether flame propagation continues across the specimen. For aircraft cabin materials, FAR 25.853 (Appendix F, Part I) requires vertically oriented specimens to self-extinguish, with average afterflame times not exceeding 15 seconds and no sustained flaming drips. Furniture and upholstery applications are frequently governed by EN 1021-1/2, BS 5852, and similar smoldering and small-flame ignition standards, while railway interior components fall under EN 45545-2 fire-safety requirements. Selecting the correct combination of tests depends on the end-use regulation and the OEM or brand technical specification.

Instrumentation, Timing Accuracy, and Reporting

Reliable afterflame time measurement requires a compliant ventilation cabinet, a burner with verified flame height and gas composition (methane, propane, or liquefied petroleum gas as specified), conditioning facilities, and timing devices with at least 0.1 s resolution. The test report should identify the standard and procedure used, specimen construction and thickness, conditioning history, direction of testing (face or back, machine or cross direction), individual and average afterflame and afterglow times, damaged length, dripping behavior, and the resulting classification or pass/fail conclusion against the specified limit. Accredited third-party laboratories ensure traceable equipment calibration and consistent operator-independent judgment of flameout, which is essential because flame extinction is visually determined.

Applications

Afterflame time test data for synthetic leather are used throughout the material supply chain and across regulated industries:

• Automotive interiors: seat covers, door trims, headliners, instrument panel skins, and gear-shift boots evaluated against GB 8410, ISO 3795, and FMVSS 302 requirements.
• Rail and urban transit: seating and interior cladding materials for metro, high-speed rail, and bus applications under EN 45545-2 and operator specifications.
• Aviation: cabin seat dress covers, armrests, and decorative laminates under FAR 25.853 and equivalent airworthiness rules.
• Furniture and upholstery: residential and contract furniture, sofa coverings, and office seating tested to EN 1021, BS 5852, and procurement standards.
• Footwear, garments, and leather goods: uppers, linings, and trims where brand flame-safety specifications and children's product regulations apply.
• Architecture and wall coverings: decorative synthetic leather panels for hotels, theaters, and public buildings subject to interior finish fire codes.
• Research and development: comparison of halogen-free flame-retardant formulations, back-coating treatments, and surface finishes to optimize self-extinguishing behavior.

FAQ

What is the difference between afterflame time and afterglow time?

Afterflame time is the period during which a specimen continues to burn with a visible flame after the ignition source is removed. Afterglow time is the period of flameless glowing combustion that may continue after the flame has gone out. Both are recorded because a material that stops flaming but continues to glow can still ignite adjacent materials.

Which standard is most commonly specified for synthetic leather afterflame time?

For coated-fabric constructions, GB/T 5455 and ASTM D6413 vertical flame tests are the most common because they directly measure afterflame time, afterglow time, and char length. When synthetic leather is qualified as a polymeric component, UL 94 / GB/T 2408 vertical classification is typically required. End-use regulations ultimately determine the applicable method.

What are typical acceptance criteria?

Acceptance limits depend on the specification: UL 94 V-0 requires individual afterflame times within 10 seconds and a set total within 50 seconds; aviation vertical tests generally limit average afterflame time to 15 seconds; and many automotive and furniture specifications require complete self-extinguishing within a few seconds with no flaming drips. Always verify the limit stated in the governing product standard or customer technical agreement.

Why do afterflame results vary between batches of the same material?

Variations can arise from flame-retardant dosage and distribution, plasticizer content, coating thickness, textile backing construction, specimen direction, moisture content from conditioning, and surface finishes or adhesives applied downstream. Strict lot control, consistent conditioning, and periodic verification testing at accredited third-party laboratories minimize variability.

Is afterflame time the same as burning rate?

No. Afterflame time measures the duration of combustion after ignition removal, whereas burning rate (used in GB 8410, ISO 3795, and FMVSS 302 horizontal tests) measures the speed of flame travel across a specimen in mm/min. Both parameters are complementary elements of a complete flammability assessment.

Do flame-retardant treatments affect other properties of synthetic leather?

High flame-retardant loading can influence softness, tensile and tear strength, hydrolysis resistance, color stability, and environmental compliance. Formulators therefore balance afterflame performance against physical-mechanical properties and restricted-substance requirements, confirming the final formulation through combined flammability and durability testing.