The synthetic leather vertical burning test is a core flammability evaluation that measures afterflame time, afterglow time, damaged length, and dripping behavior when vertically oriented specimens are exposed to a standardized ignition flame. Performed by accredited third-party laboratories in accordance with international and national standards such as ISO, ASTM, UL, GB, and FAR, this test is essential for synthetic leather used in automotive interiors, furniture upholstery, apparel, aircraft cabin components, and public-transport applications. Understanding the test principle, specimen requirements, procedures, and acceptance criteria helps manufacturers select materials and flame-retardant formulations that satisfy regulatory and customer specifications.
Technical Overview
The synthetic leather vertical burning test is a laboratory fire-resistance evaluation in which a strip of polyurethane (PU), polyvinyl chloride (PVC), or microfiber synthetic leather is suspended vertically in a draft-protected enclosure and exposed to a defined gas flame for a specified duration. Because the specimen hangs vertically, flames and hot combustion gases travel upward along the surface, which represents one of the most severe geometries for flame propagation in flexible sheet materials. The test therefore provides a conservative indication of how synthetic leather will behave when exposed to a small ignition source such as a match, cigarette lighter, or electrical short-circuit arc.
During the test, the laboratory records several quantitative parameters, including afterflame time (the period the specimen continues to burn after the ignition flame is removed), afterglow time (glowing combustion without a visible flame), damaged or char length (the distance the flame has propagated along the specimen), and whether flaming molten drips fall and ignite an indicator material such as cotton placed below the specimen. These results are used to classify the flame resistance of the material and to demonstrate compliance with fire-safety regulations for vehicles, aircraft, furniture, and public buildings.
The test is typically conducted in a stainless-steel combustion chamber equipped with a calibrated methane, propane, or butane burner, a specimen holder or clamp frame, timing devices, graduated scales, and optional marking threads that break when the flame front passes. Common reference standards include ISO 15025 and ISO 6941, ASTM D6413, NFPA 701, UL 94, GB/T 5455, and the vertical flame methods specified in FAR Part 25 Appendix F for civil aircraft cabin materials.
Testing Samples
Polyurethane (PU) Synthetic Leather
PU-coated synthetic leather is widely used in garments, footwear, upholstery, and automotive seat covers. PU is thermoplastic and may soften, shrink, or melt away from the flame, so the vertical burning test evaluates not only flame spread but also melt-drip behavior. Specimens are usually cut in both the machine direction and transverse direction because coating and fabric construction can produce anisotropic burning behavior.
Polyvinyl Chloride (PVC) Synthetic Leather
PVC leather, often plasticized and filled with flame-retardant additives such as antimony trioxide in combination with halogenated systems, is commonly submitted for vertical burning evaluation in transportation and wall-covering applications. The test verifies whether the compound formulation achieves the required self-extinguishing performance and whether plasticizer drips carry flame to the indicator cotton.
Microfiber Synthetic Leather
Microfiber (ultrafine fiber) synthetic leather, which consists of a three-dimensional fiber network impregnated with polyurethane, is tested to confirm that the dense structure, thickness, and any flame-retardant finishing meet the ignition and flame-spread limits required for premium automotive and furniture applications.
Base Fabrics, Coated Composites, and Finished Components
In addition to finished synthetic leather rolls, laboratories can evaluate the base fabric, laminated composites of synthetic leather with foam or adhesive layers, and finished components such as seat covers, door trim panels, and headrests. Testing the complete material stack is important because adhesives, backing foams, and sewing threads significantly influence the overall burning behavior.
Testing Items
Depending on the specified standard and end-use regulation, the following parameters are determined during a synthetic leather vertical burning test:
- Afterflame time: the time, in seconds, that flaming continues on the specimen after removal of the ignition flame.
- Afterglow time: the duration of glow persistence after flaming ceases, which indicates smoldering propensity.
- Damaged length (char length or burn length): the maximum distance from the point or edge of flame application to the furthest evidence of damage, measured in millimeters.
- Flame spread time: the time required for the flame front to travel between reference markers or threads on vertically oriented specimens.
- Flaming drips and molten debris: whether burning droplets or fragments fall from the specimen and whether they ignite a cotton indicator placed beneath it.
- Ignition resistance: the minimum flame application time, or ignition ease, required to establish sustained combustion when the flame is applied to the bottom edge or to the face of the specimen.
- Surface flash and hole formation: rapid flame propagation across the surface without penetration of the base structure, or the occurrence of through-holes, both of which affect classification.
Testing Methods
Sample Preparation and Conditioning
Specimens are die-cut from representative areas of the synthetic leather roll, away from selvage edges, creases, and visible defects. Typical specimen dimensions are 300 mm × 80 mm for GB/T 5455, approximately 300 mm × 76 mm for ASTM D6413, and 200 mm × 160 mm for ISO 15025, with the longer dimension aligned in the direction being tested. Most programs require at least five specimens per direction to account for variability. Before testing, specimens are conditioned in a standard atmosphere of 20 ± 2 °C and 65 ± 5 % relative humidity for a minimum of 24 hours in accordance with ISO 139 or the equivalent conditioning clause of the applicable method. For aviation tests such as FAR Part 25 Appendix F, specimens are additionally oven-dried and cooled in a desiccator to remove absorbed moisture that would otherwise delay ignition.
Test Procedure
A conditioned specimen is clamped in the vertical holder so that the lower edge hangs freely above the burner. The gas flame, typically 38 mm to 40 mm in height and adjusted using a calibrated ruler, is applied to the bottom edge or the face of the specimen for a defined period, commonly 10 seconds in ISO 15025 and 12 seconds in GB/T 5455, ASTM D6413, and FAR vertical methods. Timing of afterflame and afterglow begins the moment the ignition flame is withdrawn. After the specimen has fully extinguished and cooled, the damaged length is measured along its axis, and observations of shrinking, melting, hole formation, and flaming drips are recorded. A pad of dry absorbent cotton is positioned below the specimen whenever drip ignition must be assessed.
Applicable Standards and Typical Acceptance Criteria
Several vertical burning standards are applied to synthetic leather depending on the market and end use:
- GB/T 5455: the Chinese vertical method for textile burning behavior, widely applied to coated fabrics and synthetic leather; common grading limits used in interior decoration codes require damaged length ≤ 150 mm, afterflame time ≤ 5 s, and afterglow time ≤ 5 s with no flaming melt drips for the higher flame-retardant classes.
- ISO 15025 / EN ISO 15025: limited flame spread methods with surface (Procedure A) and bottom-edge (Procedure B) ignition using a 10-second flame, frequently referenced for protective-clothing and contractual specifications.
- ISO 6940 and ISO 6941: methods for ignition ease and flame spread time on vertically oriented specimens using marker threads.
- ASTM D6413: the vertical flame resistance method derived from federal textile test methods, reporting afterflame, afterglow, char length, and cotton ignition.
- NFPA 701: small-scale and large-scale flame propagation tests for textiles and films, assessing flameout time, mass loss, and flaming debris for applications such as drapery and wall coverings.
- UL 94 vertical classifications (V-0, V-1, V-2): applied to plastic materials and some flexible sheet products, with V-0 requiring individual afterflame times ≤ 10 s and no flaming drips that ignite cotton.
- FAR Part 25 Appendix F Part I: the 12-second and 60-second vertical tests for aircraft cabin materials, with classic 12-second criteria of average burn length ≤ 203 mm, average afterflame time ≤ 15 s, and drips that extinguish within a few seconds.
- Related automotive methods such as FMVSS 302, GB 8410, and ISO 3795: although horizontal in orientation, they are frequently tested alongside vertical methods when OEM specifications require additional assurance for seat and door-trim materials.
Applications
Vertical burning test reports for synthetic leather are used across many regulated industries:
- Automotive interiors: seat covers, door panels, headliners, instrument panel skins, and gear-shift boots, supporting compliance with OEM flammability specifications and national vehicle interior material regulations.
- Furniture and upholstered seating: office chairs, sofas, theater and stadium seating, and contract furniture, where synthetic leather must resist small open-flame ignition sources.
- Apparel and accessories: jackets, linings, gloves, belts, and bags, particularly for workwear and uniforms where limited flame spread classifications are specified.
- Aircraft and rail interiors: cabin sidewalls, seat dress covers, armrest covers, and trim materials evaluated against aviation vertical burn requirements.
- Public buildings and interiors: wall coverings, upholstery in hotels, hospitals, and cinemas, and decorative elements subject to interior finishing material fire codes.
- Footwear and luggage: flame-resistance verification for products sold into markets with flammability requirements for coated fabrics.
- Product development and quality control: comparing flame-retardant formulations, backing fabrics, coating recipes, and post-treatment processes before mass production.
FAQ
What is the synthetic leather vertical burning test?
It is a flammability test in which a vertically suspended specimen of synthetic leather is exposed to a standardized gas flame for a fixed time. The laboratory measures afterflame time, afterglow time, damaged length, flame spread, and dripping behavior to classify the flame resistance of the material according to standards such as GB/T 5455, ISO 15025, ASTM D6413, NFPA 701, UL 94, and FAR Part 25 Appendix F.
Why is the vertical orientation considered more severe than the horizontal one?
In the vertical position, the flame burns upward, preheating the unburned material above the flame front through convection and radiation. This accelerates flame propagation, increases melt dripping, and generally produces longer damaged lengths than horizontal methods such as FMVSS 302 or GB 8410, making the vertical test a stricter screen for material safety.
How many specimens are required and how are they prepared?
Most standards require a minimum of five specimens cut in each principal direction of the synthetic leather. Specimens are conditioned at 20 ± 2 °C and 65 ± 5 % relative humidity for at least 24 hours, and aviation test programs additionally require oven drying and desiccator cooling before ignition.
What results may cause a specimen to fail?
Typical failure indicators include afterflame times exceeding the specified limit, damaged lengths beyond the maximum allowed, flames reaching the top edge or side edges of the specimen, and flaming molten drips that ignite the cotton indicator placed beneath the specimen.
How can the vertical burning performance of synthetic leather be improved?
Manufacturers can optimize the flame-retardant package in the polymer coating, select inherently flame-resistant base fabrics, increase coating thickness, use halogen-antimony or phosphorus-based synergistic systems, apply back coatings or flame-retardant finishes, and avoid combustible adhesive and foam layers in the material stack. Verification through retesting at an accredited third-party laboratory is essential after any formulation change.
Is the vertical burning test sufficient for full fire-safety compliance?
It is one component of a complete evaluation. Depending on the application, synthetic leather may also need to pass horizontal burn rate tests, cigarette and match ignition tests, smoke density and toxicity assessments, oxygen index determination, and cone calorimetry. Buyers should confirm the exact test matrix with the relevant regulation, end customer, or procurement specification before submitting samples.