ISO 9773 Thin Flexible Plastic Vertical Burning Test | United Test Flammability Testing Machine

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ISO 9773 Burning Behaviour Tester for Thin Flexible Plastics | UnitedTest

UnitedTest manufactures ISO 9773 testing machines to determine burning behaviour of thin flexible vertical plastic specimens with small flame ignition, measuring afterflame time and afterglow time for flammability screening.

ISO 9773 Plastics — Determination of burning behaviour of thin flexible vertical specimens in contact with a small flame ignition source

ISO 9773 specifies a small‑scale laboratory screening method to evaluate relative burning performance of thin, flexible vertically‑oriented plastic specimens exposed to a low‑energy small‑flame ignition source. These thin flexible samples distort or shrink away from flame in IEC 60695‑11‑10 Method B and cannot be evaluated by that vertical‑burn procedure. The test measures afterflame time and afterglow time to assess flammability performance for thin flexible plastic materials used in electrical, packaging and construction industries.

Test principle

A nearly cylindrical lapped test specimen is held vertically at its upper end. Its free lower end receives two successive controlled 3‑second flame applications from a calibrated 20 mm‑height 50 W burner flame. After each flame removal, technicians record afterflame duration; after the second flame exposure, afterglow time is also captured. Burning‑related observations include whether flame/glow reaches the 125 mm marked line and whether underlying cotton‑wool indicator is ignited by molten dripping material. Burning behaviour is quantified by these timing and visual metrics.

Test Specimen Information

Standard geometry: 200 mm ± 5 mm long × 50 mm ± 2 mm wide × max 0.25 mm thick; thickness of each specimen measured to 0.01 mm .
Thicker than 0.25 mm is still permitted if the specimen, because of thinness/non‑rigidity, distorts, shrinks, or is consumed up to the holding clamp when tested by IEC 60695‑11‑10 (i.e. the rigid‑specimen test is invalid).
Preparation: mark a line across the width at 125 mm ± 5 mm from the bottom end; wrap the longitudinal axis tightly around the 13 mm mandrel to form a lapped cylinder with the 125 mm line exposed; secure the overlapping portion within the upper 75 mm and at the upper end with tape; remove the mandrel. For stiff films, nichrome wire wound around the top 75 mm ± 2 mm is recommended instead of/in addition to tape.
Quantity: minimum 20 specimens (2 sets of 5 per each of the two conditioning treatments); extra specimens advisable for retesting.

ISO 9773 Thin Flexible Plastic Vertical Burning Test

Test equipment required for ISO 9773 Thin Flexible Plastic Vertical Burning Test

Recommend UntiedTest UL94 Horizontal & Vertical Flame Tester, consist of below:

Test chamber / fume hood	Minimum internal volume 0.5 m³, draught‑free during test, dark inner surfaces, internal light level < 20 lux; exhaust fan activated only after testing to vent toxic combustion fumes
50 W laboratory diffusion burner	Barrel length 100 mm ± 10 mm, inner diameter 9.5 mm ± 0.3 mm, no stabilizer attachment, calibrated following IEC 60695‑11‑5 and IEC 60695‑11‑10
Adjustable ring‑stand with clamps	For vertical specimen mounting; spring clamp grips upper 6 mm of specimen to close tube top and prevent chimney‑effect airflow inside cylindrical sample
Timing device	Stopwatch or timer; accuracy 0.5 s per hour, resolution 0.1 s; record times to nearest second in practice
Measuring scale & micrometer	Millimetre‑graduated ruler; micrometer readable to 0.01 mm for specimen‑thickness measurement
Fuel gas	Technical‑grade methane (minimum 98 % purity); alternative gas shall have heat content 37 MJ/m³ ± 1 MJ/m³; methane is mandatory in case of dispute
Desiccator	Maintain relative humidity ≤ 20 % at 23 °C ± 2 °C, filled with anhydrous calcium chloride or equivalent desiccant; for cotton‑wool and specimen conditioning
Air‑circulating oven	Maintain 70 °C ± 2 °C, minimum 5 air changes per hour for thermal‑ageing pre‑treatment of specimens (7‑day oven conditioning)
Mandrel rod	Diameter 13 mm ± 0.5 mm for rolling flat plastic film into lapped cylindrical specimens

Key Test Parameters

Flame	20 mm ± 1 mm, yellow‑tipped blue flame; increase air until the yellow tip just disappears, re‑check height
Burner position	Burner top 10 mm ± 1 mm below the mid‑point of the bottom edge of the unlapped section
Flame application	3 s ± 0.5 s, applied twice (second application starts as soon as the first afterflame ceases)
Burner withdrawal	≈ 300 mm/s to a distance ≥ 150 mm
Dripping provision	Burner may be tilted up to 45° and withdrawn to keep drips out of the barrel while maintaining the 10 mm spacing (ignore molten strings)
Specimen mounting	Clamped from the upper 6 mm, longitudinal axis vertical, top of tube closed (prevents chimney effect)
Cotton indicator	0.05–0.08 g, ≈ 50 mm × 50 mm, max 6 mm thick, placed 300 mm ± 10 mm below the specimen's lower end
Laboratory atmosphere	15–35 °C, 45–75 % RH
Conditioning A	2 sets × 5 specimens: ≥ 48 h at 23 °C ± 2 °C / 50 % ± 10 % RH; test within 1 h
Conditioning B	2 sets × 5 specimens: 168 h at 70 °C ± 2 °C, then cool in desiccator ≥ 4 h at room temperature; test within 1 h
Timing resolution	Record to the nearest second

Test procedure of ISO 9773 Thin Flexible Plastic Vertical Burning Test

1. Mount the cylindrical specimen vertically by clamping its top 6 mm; specimen bottom sits 300 mm ± 10 mm vertically above the cotton‑wool indicator pad laid horizontally underneath the sample.

2. Adjust burner flame to obtain 20 mm ± 1 mm blue flame with yellow tip eliminated. Position burner outlet 10 mm ± 1 mm directly below specimen bottom‑edge mid‑point of the non‑lapped section.

3. First‑flame application: apply flame centrally to specimen bottom edge for 3 s ± 0.5 s. If molten dripping occurs, tilt burner up to 45° to avoid molten material falling into burner barrel while preserving the 10 mm distance from burner outlet to specimen main body. Immediately withdraw burner at ~300 mm/s to ≥ 150 mm away and start timing for first afterflame time t₁ as soon as flame source is pulled away, record t₁.

4. Right after first afterflame extinguishes, re‑position burner under specimen for the second flame exposure of 3 s ± 0.5 s, again managing dripping as required by procedure.

5. Second‑flame completion: withdraw burner rapidly again; simultaneously start timing second afterflame time t₂ and afterglow time t₃. Record t₂, t₃; document observations: whether flame/afterglow propagates to the 125 mm mark; whether cotton‑wool indicator is ignited by burning drips or particles.

6. Repeat the whole test sequence for each specimen until each 5‑specimen group is fully completed.

Industry Application Fields

ISO 9773 / UL 94 VTM is the reference flammability gate for any thin, flexible polymeric material that will live next to a heat or ignition source:
Electronics & electrical: flexible printed circuits (FPC/FPCBs), insulating films (PI, PET, PEN), cable/wire wrap and insulation tapes, heat‑shrink tubing, battery pouch/separator films, connector and transformer insulation, flexible displays and printed electronics .
Appliances & HVAC: internal insulation films, flexible ducting, labels and nameplates.
Automotive & transport: interior decorative films, wiring‑harness tapes, air‑bag/lightweight films (often in combination with FMVSS 302 / ISO 3795 for horizontal burn).
Packaging & converting: barrier films, laminates, coated/lacquered films, shrink and stretch films.
Other: medical pouches and tubing, textiles and coated fabrics, adhesive tapes, release liners, building/vapour‑barrier membranes.

Typical use cases: material pre‑selection in R&D, incoming‑quality control and batch‑to‑batch consistency, verification of flame‑retardant masterbatch level, and generating data for UL Yellow Cards / OEM material specifications .

Related Test Standard:

IEC 60695‑11‑10	50 W horizontal & vertical flame test methods
UL 94 Section 11 (VTM‑0/‑1/‑2)	same cylinder specimen, 20 mm flame, two 3 s applications, VTM categories. The two are used for the same purpose, though certification requirements can differ
ASTM D635	US horizontal‑burning rate test for plastics (similar to ISO 1210 Method A).
ISO 1210	Plastics; determination of the burning behaviour of horizontal and vertical specimens in contact with a small-flame ignition source
IEC 60695‑11‑20	500 W flame (5V classifications), the "bigger flame" counterpart.
IEC 60695‑11‑4 IEC 60695‑11‑5	50 W flame apparatus/confirmation and needle‑flame apparatus & calibration (normative for burner calibration)
ISO 9773	vertical burning of thin flexible films/sheets (for materials that shrink away, which ISO 1210 cannot handle).
ISO 9772	cellular plastics, horizontal small‑flame burning.
ASTM D3801	Vertical test for rigid specimens (two 10 s applications) — the counterpart you must not use for thin films
ASTM D4804	US equivalent method for non‑rigid solid plastics; same 200 × 50 mm cylinder, 13 mm mandrel, two 3 s applications, VTM‑0/‑1/‑2
GB/T 2408 (China), AS/NZS 60695.11.10, JIS C 60695‑11‑10, UNE‑EN 60695‑11‑10 — national adoptions of IEC 60695‑11‑10.

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UL94 horizontal vertical flame tester, standard UL94 flammability test chamber for plastic, rubber, foam, electronic material fire resistance test, supports HB/V0/V1/V2/5VA/5VB/VTM/HBF test grades, PLC touch screen automatic timing, 50W & 500W dual burner, 1-year full warranty, factory direct export

Oxygen Index Apparatus/LOI tester (Limitation Oxygen Index tester) is widely used to measure burning performance of plastics, rubber, fiber, foam,,film etc., The technique measures the minimum percentage of oxygen in the test atmosphere that is required to marginally support combustion.

1. What is the ISO 9773 test?

ISO 9773:2024 is a small‑scale laboratory screening procedure that compares the relative burning behaviour of thin, relatively flexible plastics held vertically and exposed to a low‑energy (20 mm, 50 W) flame. It measures afterflame times t₁ and t₂ plus afterglow time t₃, and optionally classifies the material as VTM‑0, VTM‑1 or VTM‑2 (Annex A).

2. Why can’t thin films be tested with the normal UL 94 V test?

Because they distort, curl or shrink away from the applied flame without igniting. A flat thin film escapes the flame and yields a falsely favourable result. ISO 9773 rolls the film into a lapped cylinder on a 13 mm mandrel so it cannot curl away, and applies the flame for only 3 s (instead of 10 s) per application.

3. What thickness of material does ISO 9773 cover?

The standard specimen is a maximum of 0.25 mm thick, measured to 0.01 mm. Specimens thicker than 0.25 mm may still be tested by this method if, because of their thinness and non‑rigidity, they distort, shrink or are consumed up to the holding clamp when tested by IEC 60695‑11‑10.

4. What are the differences between VTM‑0, VTM‑1 and VTM‑2?

VTM‑0: each afterflame ≤ 10 s, total set afterflame ≤ 50 s, afterglow ≤ 30 s, no burn to the 125 mm mark, no cotton ignition. VTM‑1: ≤ 30 s / ≤ 250 s / ≤ 60 s, no cotton ignition. VTM‑2: same time limits as VTM‑1 but flaming drips are allowed to ignite the cotton indicator. VTM‑0 is the highest level of flame resistance of the three.

5. Is ISO 9773 the same as UL 94 VTM?

They are closely aligned and used for the same purpose — same cylindrical specimen, 13 mm mandrel, 20 mm flame and two 3 s applications, with VTM‑0/‑1/‑2 classifications. Certification requirements can differ, so always check which document your customer or certification body cites. ASTM D4804 is the US equivalent method, and GB/T 40302‑2021 is the Chinese adoption of ISO 9773:1998.

6. Which gas is required for the burner?

Technical‑grade methane of minimum 98 % purity, supplied through a regulator and flow meter. Other gas mixtures with a heat content of 37 MJ/m³ ± 1 MJ/m³ have been found to give similar results, but methane ≥ 98 % must be used in cases of dispute.

7. How many specimens are needed?

A minimum of 20 specimens: two sets of five for conditioning at 23 °C ± 2 °C / 50 % ± 10 % RH for at least 48 h, and two sets of five for conditioning at 70 °C ± 2 °C for 168 h followed by at least 4 h cooling in a desiccator. Additional specimens should be prepared for possible retesting.

8. What does the cotton wool indicator do?

A layer of 0.05 g to 0.08 g of 100 % absorbent cotton wool (≈ 50 mm × 50 mm, ≤ 6 mm thick) is placed 300 mm ± 10 mm below the specimen. If flaming particles or molten drops falling from the specimen ignite it, the material cannot be classified VTM‑0 or VTM‑1 — it is VTM‑2 at best. The cotton must be kept in a desiccator for at least 24 h and used within 30 min of removal.

9. Why is the chamber required to be dark (below 20 lux)?

A low, controlled background light level makes the flame, afterglow and small flaming drips clearly visible and makes observations reproducible between operators and laboratories. It was added as an explicit requirement in the 2024 edition: a light meter placed in the specimen position, facing the rear of the chamber, must read less than 20 lux.

10. How do I choose an ISO 9773 tester?

Check five things: (1) chamber ≥ 0.5 m³ with verified < 20 lux and an exhaust interlock; (2) a genuine 50 W diffusion burner to ISO 10093 with 100 mm barrel and 9.5 mm bore, plus a flame‑calibration kit; (3) automatic 3 s double flame application with burner positioning at 10 mm ± 1 mm and the 45° tilt provision for dripping; (4) 0.1 s timing and automatic calculation of total afterflame time; (5) the full accessory set (13 mm mandrel, spring clamp, mandrel‑wound specimen jig, cotton‑wool holder) plus optional 23 °C/50 % RH and 70 °C conditioning equipment.

11: What key observations do I need to record besides afterflame and afterglow time?

Test report shall document:

1. Whether afterflame / afterglow propagates up to the 125 mm marked line on specimen;

2. Whether cotton‑wool indicator pad underneath is ignited by molten or flaming drips;

3. Individual specimen thickness, all pre‑conditioning information, any deviation from test procedure, abnormal burning phenomenon.

12: What is the difference between ISO 9773 and IEC 60695‑11‑10 (UL 94 V‑0/V‑1/V‑2)?

- IEC 60695‑11‑10 (UL 94 V‑rating): For rigid, self‑supporting plastic samples. Thin flexible films shrink away and give invalid test results.

- ISO 9773: Specially for thin non‑rigid flexible films, uses rolled cylindrical specimen form and VTM‑0/VTM‑1/VTM‑2 classification instead of V‑ratings.

13: Why is ISO 9773 important for material manufacturers and laboratories?

Conventional vertical‑burn tests fail for thin flexible polymer films because specimens retract from flame source. ISO 9773 uses a lapped cylindrical specimen preparation to hold thin films for valid vertical flame exposure. It lets users compare flammability grades, check batch‑to‑batch consistency, evaluate flame‑retardant additive performance, and assess burning‑property shift after thermal ageing. The VTM classification supports material selection for electronics, insulation and flexible component design. Important note: it is only laboratory‑scale comparative screening and cannot directly evaluate real‑world end‑product fire hazard.

14: Why choose ISO 9773 Flammability Test Machine, Thin Flexible Plastic Vertical Burning Test Machine made by UnitedTest?

UnitedTest manufactures professional ISO 9773:2024 flammability tester for thin flexible plastic films & sheets. Perform VTM‑0, VTM‑1, VTM‑2 vertical burning test for non‑rigid polymer samples that cannot run IEC 60695‑11‑10 test. Complete with test chamber, calibrated 50 W burner, timing system, specimen mandrel & cotton‑wool test accessories. Suitable for QC lab, R&D and third‑party testing laboratories worldwide.

UnitedTest is a trusted manufacturer of ISO 9773 vertical burning test equipment, fully complying with latest ISO 9773:2024 international standard for thin flexible plastics flammability assessment.

Our ISO 9773 tester is purpose‑built for thin, non‑rigid plastic films, foils and flexible polymer sheets which distort or shrink away from flame and cannot get valid test results on standard UL 94 / IEC 60695‑11‑10 vertical flame testers.

Key machine features:

Dark‑interior draught‑free test enclosure ≥ 0.5 m³ with exhaust fan; internal light level controlled below 20 lux as required by ISO 9773.
Calibrated 50 W diffusion burner for stable 20 mm test flame; supports methane fuel with gas flow regulator
High‑precision timing system (0.1 s resolution) for measuring afterflame time t₁, t₂ and afterglow time t₃.
Complete specimen preparation accessories: 13 mm specimen mandrel, nichrome wire, pressure‑sensitive tape, cotton‑wool test kit
Adjustable specimen clamping stand to create lapped cylindrical test‑sample geometry
Observation window for monitoring burning behaviour, dripping particles and cotton‑wool ignition status

Typical applications:Flexible electronic insulating films, polymer packaging foils, decorative plastic sheets, thin membrane materials, flexible component materials for consumer and industrial products. Supports quality‑control batch inspection, new‑material R&D pre‑selection and VTM‑0 / VTM‑1 / VTM‑2 classification testing.

UnitedTest ISO 9773 test machines are widely used in polymer factories, electrical‑component manufacturers, university research labs and third‑party fire‑safety testing institutes globally. We supply complete instrument, operation manual aligned to ISO 9773:2024 standard, installation guidance and after‑sales technical support.

We offer customization to meet your specific needs. Our expert team will collaborate with you to develop the perfect product for you