Determination of Smoldering Time (Afterglow Time) of Synthetic Leather: Test Methods, Standards, and

Smoldering time determination for synthetic leather is a fundamental fire-safety test that measures how long a PU, PVC, or microfiber leather material continues to glow and combust without an open flame after the ignition source is removed. This guide explains the combustion principles, applicable ISO, GB, EN, ASTM, UL, and JIS standards, specimen preparation requirements, step-by-step test procedures, and typical acceptance criteria for automotive, furniture, footwear, and apparel applications.

Technical Overview

Synthetic leather—including polyurethane (PU), polyvinyl chloride (PVC), and microfiber constructions—is a polymer-coated or polymer-impregnated textile composite widely used in automotive interiors, furniture, footwear, luggage, and apparel. Because these applications carry fire-hazard exposure, flammability performance is regulated, and one of the most important measurable parameters is smoldering time, more precisely termed afterglow time in vertical burn standards such as GB/T 5455.

Smoldering is a slow, flameless, glowing combustion that propagates through the solid phase of a material, often along the cellulosic or thermally degraded textile backing of synthetic leather. Afterglow time is defined as the duration for which a specimen continues to glow after flaming has ceased (or after the ignition source is removed). Prolonged afterglow is a recognized fire hazard because it can act as a residual ignition source, cause delayed re-ignition, generate carbon monoxide, and extend fire growth even when visible flaming has stopped.

Smoldering time determination is therefore integrated into flammability evaluation frameworks published by standards organizations including ISO, IEC, GB (Chinese national standards), EN, ASTM, UL, and JIS. Testing is typically performed by manufacturers' in-house laboratories or by accredited third-party laboratories for regulatory submission and certification.

• Core measurand: afterglow (smoldering) time, recorded in seconds from cessation of flaming to complete extinction of glow.
• Companion parameters: afterflame time, damaged (char) length, burning rate, ignition response, and flaming drip behavior.
• Key methods: vertical strip burning, horizontal burning, automotive interior burning, and smoldering cigarette ignition source tests.
• End-use drivers: automotive interiors, upholstered furniture, public-venue decorative materials, apparel, and footwear.

Testing Samples

Polyurethane (PU) Synthetic Leather

PU synthetic leather produced by dry or wet processing on knitted or woven textile backings is tested in its finished, coated state. Because the urethane top layer and the fabric substrate respond differently to heat, specimens must be tested in both machine (lengthwise) and transverse (crosswise) directions to capture directional smoldering behavior.

Polyvinyl Chloride (PVC) Synthetic Leather

PVC materials contain plasticizers and stabilizers that soften and melt before or during decomposition. Testing evaluates whether the material drips, forms char that supports afterglow, or spreads smoldering along the fabric reinforcement. Both unsupported and fabric-backed PVC constructions are within scope.

Microfiber Synthetic Leather

Microfiber (sea-island or split-fiber) synthetic leather has a dense three-dimensional fiber structure that can sustain prolonged smoldering if the polymer matrix degrades into combustible char. Flame-retardant grades are commonly evaluated for automotive and high-end footwear applications.

Specimen Preparation and Conditioning

Specimens are cut to the dimensions required by the selected method, free of creases and visible defects, and taken at least 50 mm from fabric edges and away from seams. Replicate counts vary by standard—vertical burn testing typically requires five specimens per direction (ten in total), while horizontal automotive tests generally require three to five specimens plus spares. Conditioning requirements include:

• Standard atmosphere of 20 ± 2 °C and 65 ± 4 % relative humidity until moisture equilibrium is reached, commonly a minimum of 24 hours.
• Marking of gauge lines or reference points for damaged length and burning rate measurement where required.
• Testing in the as-received state unless a specific preconditioning, washing, or accelerated aging treatment is specified by the product standard or the buyer.

Testing Items

Smoldering time determination is generally conducted as part of a complete flammability profile. The testing items most commonly reported for synthetic leather include:

• Afterglow (smoldering) time in seconds, measured to the nearest second until all glowing ceases.
• Afterflame time in seconds, the period of continued flaming after removal of the ignition flame.
• Damaged length (char length) in millimeters, measured along the specimen axis from the original edge to the furthest damaged point.
• Linear burning rate in millimeters per minute, calculated as sixty times the burned distance divided by the elapsed time.
• Time to ignition under a defined ignition source.
• Occurrence of surface flash, flaming molten drips, or incandescent debris.
• Pass/fail classification or flame-retardancy grading, for example UL 94 V-0/V-1/V-2 classes or B1/B2 flame-retardant grades under Chinese product standards.

Testing Methods

Vertical Burn Method (GB/T 5455)

The vertical method is the primary procedure for afterglow time determination on flexible coated fabrics and synthetic leather. A specimen of 300 mm × 80 mm is hung vertically in a draft-protected chamber, and a standardized propane flame of 40 ± 2 mm height is applied to the lower edge for 12 ± 0.2 seconds. After the burner is withdrawn, the operator records the afterflame time, then continues timing until the final glow disappears—this interval is the afterglow (smoldering) time. Damaged length is subsequently measured to the nearest millimeter. Results are reported as maximum and mean values for each specimen direction, and the same principle is reflected in related vertical procedures such as ISO 6941 for flame spread on vertical fabrics.

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

For thinner synthetic leather sheets and trim components, 125 mm × 13 mm bar specimens are tested horizontally (HB class) or vertically (V classes). In the vertical V-classification, a 20 mm blue flame is applied twice for ten seconds each to the free lower end. Classification limits for V-0, for example, require individual afterflame times no greater than ten seconds, a total afterflame time no greater than 50 seconds for the full set, afterglow extinction within 30 seconds after the second application, and no flaming drips that ignite indicator cotton. Glowing combustion and its duration are explicitly recorded as part of the classification logic.

Automotive Interior Horizontal Burn (GB 8410, FMVSS 302, ISO 3795, JIS D 1201)

Synthetic leather used for vehicle seats, door panels, and headliners is evaluated with a horizontal burner apparatus. A specimen of 356 mm × 102 mm is mounted horizontally in a U-shaped frame with the free end exposed to a 38 mm flame for 15 seconds. The test determines the time for the flame front to travel between gauge marks and the burning rate, calculated as sixty times the burned distance in millimeters divided by the burning time in seconds. The regulatory limit is a burning rate not exceeding approximately 100 mm/min, or self-extinguishment before the flame front reaches the first gauge mark. Observers also record any continuing glow, afterflame, and flaming drops after the specimen is removed from the frame.

Smoldering Ignition Source Method (EN 1021-1, BS 5852, CAL TB 117-2013)

For upholstered furniture and seating applications, smoldering propensity is assessed with a lit standard cigarette placed in the crevice between the synthetic leather cover fabric and standard filling. The assembly is observed for a defined period, commonly 60 minutes after ignition. The material passes if no progressive smoldering or flaming occurs and any localized glow self-extinguishes within the observation window; the elapsed smoldering duration and char extent are documented. This method directly addresses real-world smoldering ignition risk rather than afterglow following open-flame exposure.

General Test Procedure

• Condition the specimens to equilibrium in the standard atmosphere and verify chamber ventilation, burner cleanliness, and gas supply.
• Confirm and adjust the ignition flame height using the gauge specified by the method.
• Mount the specimen in the appropriate frame with correct orientation, gauge marks, and alignment to the burner.
• Apply the ignition flame for the prescribed exposure time, then withdraw the burner smoothly without extinguishing any flame on the specimen.
• Start the timer on withdrawal; record the afterflame time when flaming stops, and continue timing until the last visible glow disappears to obtain the afterglow (smoldering) time.
• Measure damaged length or burned distance, note drips or debris, and repeat for all replicates in both directions.
• Calculate means and maxima, apply the classification rules of the governing standard, and report results with test conditions, gas type, and any deviations.

Applications

Smoldering time data supports regulatory compliance, product certification, and material development across every major synthetic leather end market.

• Automotive interiors: seat covers, door trims, headliners, steering-wheel wraps, and gear boots tested against GB 8410, FMVSS 302, ISO 3795, and JIS D 1201 requirements.
• Furniture and upholstery: synthetic leather cover materials for sofas, office chairs, and contract seating evaluated with EN 1021-1, BS 5852, and CAL TB 117-2013 smoldering sources.
• Public transport, aviation, and marine interiors: decorative and seating materials qualified under applicable transport fire-safety codes, where afterflame and afterglow limits are strictly controlled.
• Apparel and footwear: garments, linings, and shoe uppers assessed with vertical or 45-degree methods and flame-retardant product grade requirements.
• Interior decoration: wall coverings, screens, and soft furnishings for hotels, cinemas, and public venues that must meet flame-retardant classification levels.
• Quality control and R&D: screening flame-retardant formulations, verifying incoming material consistency, and monitoring performance after washing, abrasion, or accelerated aging.

FAQ

What is the difference between afterflame time and afterglow (smoldering) time?

Afterflame time is the period during which a specimen continues to burn with a visible flame after the ignition source is removed. Afterglow, or smoldering, time begins when flaming ceases and measures how long the specimen continues to glow without flame. A material can pass an afterflame criterion yet fail an afterglow criterion, so both parameters are reported together.

Which standard should be selected for synthetic leather testing?

Selection follows the end use and target market: GB 8410, FMVSS 302, ISO 3795, or JIS D 1201 for automotive interiors; EN 1021-1, BS 5852, or CAL TB 117-2013 for furniture; GB/T 5455 for general vertical afterflame, afterglow, and damaged length determination; and GB/T 2408, IEC 60695-11-10, or UL 94 for small-scale classification of components. Buyers' specifications frequently dictate the exact method.

What sample size and quantity are required?

Vertical burn testing typically requires 300 mm × 80 mm specimens, generally five per direction. Automotive horizontal testing uses 356 mm × 102 mm specimens, usually three to five samples. Small-scale UL 94 or GB/T 2408 testing uses 125 mm × 13 mm bars, typically five specimens per classification series. Accredited third-party laboratories should always be consulted for exact quantities, as spares and retests must be anticipated.

What are typical acceptance criteria?

Examples include afterglow extinction within 30 seconds for a UL 94 V-0 classification, automotive burning rates not exceeding approximately 100 mm/min, no progressive smoldering under EN 1021-1 cigarette ignition, and, under Chinese flame-retardant textile grades, afterflame and afterglow times on the order of five seconds or less with limited damaged length for the highest grade. The governing product standard always prevails.

Which material factors influence smoldering time results?

Key influences include the fiber composition of the backing (cellulosic substrates sustain longer afterglow than polyester or nylon), total thickness and coating continuity, phosphorus- and nitrogen-based flame-retardant treatments, plasticizer content in PVC systems, moisture content after conditioning, specimen direction, and any washing or aging prior to testing.

How should testing be arranged for compliance purposes?

For regulatory submissions, certification, and buyer acceptance, testing should be performed by accredited third-party laboratories under the exact method version cited in the applicable regulation or contract. Reports should state the standard, specimen orientation, conditioning history, ignition parameters, individual and mean results for afterflame time, afterglow time, and damaged length or burning rate, together with a clear pass/fail conclusion.