V-2 flame retardancy rating testing is a vertical burning test performed under UL 94 and IEC 60695-11-10 to evaluate how quickly plastic materials self-extinguish after exposure to a small open flame and whether they release flaming drips. This guide explains the V-2 testing standards, sample requirements, test procedures, acceptance criteria, and typical applications in the electronics, appliance, and electrical equipment industries. Understanding V-2 testing helps manufacturers select compliant flame-retardant materials, verify supplier declarations, and accelerate product safety certification and market access.
Technical Overview
The V-2 flammability rating is a material classification defined in UL 94, the Standard for Tests for Flammability of Plastic Materials for Parts in Devices and Appliances, and its international equivalent IEC 60695-11-10 (Test methods 50 W horizontal and vertical flame propagation). In this test, a bar-shaped plastic specimen is clamped in a vertical orientation and exposed twice to a small gas flame. A material earns the V-2 classification when every specimen self-extinguishes within 30 seconds after each flame application, when the cumulative afterflame time of all ten specimens does not exceed 250 seconds, and when the material may release flaming droplets or particles that briefly ignite a cotton indicator placed beneath the specimen.
V-2 is the lowest of the UL 94 vertical burning classifications and sits below V-1 and V-0 in terms of drip behavior. The complete hierarchy of UL 94 small-flame classifications is:
- 5VA and 5VB – the most stringent classifications, using a 500 W flame applied to bars and plaques, with no burning through the plaque for 5VA
- V-0 – afterflame time no greater than 10 seconds per application, total afterflame time no greater than 50 seconds, no flaming drips
- V-1 – afterflame time no greater than 30 seconds per application, total afterflame time no greater than 250 seconds, no flaming drips
- V-2 – afterflame time no greater than 30 seconds per application, total afterflame time no greater than 250 seconds, flaming drips permitted
- HB – horizontal burning classification for materials that burn slowly or self-extinguish in a horizontal orientation
The single technical distinction between V-1 and V-2 is dripping behavior: a V-1 material must not produce flaming particles that ignite the cotton indicator, while a V-2 material may do so. Both ratings require identical extinguishing performance. This difference is critical for product safety assessments, because flaming drips can propagate fire to components or surfaces located below the material.
Testing Samples
Engineering Thermoplastics and Compounds
V-2 testing is routinely performed on raw polymer materials and flame-retardant compounds submitted as injection-molded plaques or bars. Common material families include ABS, polycarbonate (PC), PC/ABS blends, polypropylene (PP), polyethylene (PE), rigid PVC, polyamide 6 and 66 (PA6/PA66), PBT, PET, POM, modified PPO/PPE, and various thermoplastic elastomers. Compounders and resin producers use V-2 data to characterize the flammability performance of specific grades at defined thicknesses.
Finished Parts and Components
End-product manufacturers submit finished components cut or molded into test bars, including enclosures and covers, connectors, terminal blocks, coil bobbins, switch housings, fan blades, cable ties, bezels, wiring accessories, and structural brackets. Testing the actual production material is essential because pigments, fillers, glass fiber content, regrind ratio, and molding conditions can all shift the flammability classification relative to the resin supplier's datasheet value.
Sample Dimensions and Conditioning Requirements
Vertical burn specimens must measure 125 mm in length by 13 mm in width, cut at the thickness used in the end-use application or molded as standard plaques. Typical evaluated thicknesses include 3.2 mm, 1.6 mm, and 0.8 mm, since thinner sections burn more readily. Two sets of five specimens are required for each thickness, with additional spares recommended for potential retests. Before testing, specimens must be conditioned for at least 48 hours at 23 ± 2 °C and 50 ± 10 % relative humidity; where specified, an additional conditioning sequence of 168 hours at 70 °C followed by cooling in a desiccator may be applied.
Testing Items
During a V-2 test campaign, the laboratory records and evaluates the following parameters for every specimen:
- Afterflame time t1 – the duration of continued flaming after removal of the first flame application
- Afterflame time t2 – the duration of continued flaming after removal of the second flame application
- Afterglow time t3 – the duration of glowing combustion without flame after the second application
- Combined afterflame and afterglow time (t2 + t3) for each specimen
- Total afterflame time for each five-specimen set and for both sets combined
- Whether flaming droplets or particles fall and ignite the cotton indicator
- Whether afterflame or afterglow reaches the holding clamp or consumes the specimen
- Qualitative observations such as dripping without flame, deformation, charring, and sample shrinkage
Testing Methods
Test Apparatus and Environment
Testing is conducted in a ventilated fume chamber or enclosed test cabinet large enough to prevent drafts from disturbing the flame. A Tirrill-type laboratory burner fueled with methane or propane produces a 20 mm high blue flame of nominal 50 W power, conforming to the apparatus requirements of IEC 60695-11-4. Each specimen is clamped vertically on a ring stand with its long axis horizontal... with its lower edge positioned so the burner tube top is 10 mm below the specimen. A pad of dry, absorbent 100 % cotton approximately 6 mm thick and 50 mm × 50 mm in area is placed 300 mm below the bottom edge of the specimen to catch and record flaming drips.
Vertical Burning Test Procedure
The test sequence for each specimen follows the standardized procedure:
- Mount the conditioned specimen vertically and confirm the blue flame height is adjusted to 20 mm
- Apply the flame to the midpoint of the specimen's lower edge for 10 ± 0.5 seconds, then withdraw the burner
- Record afterflame time t1, noting any flaming drips and cotton ignition
- Once afterflame ceases, immediately reapply the flame for a second 10 ± 0.5 second interval, then withdraw the burner
- Record afterflame time t2, afterglow time t3, and whether flaming drips ignite the cotton
- Repeat for all five specimens in the first set, then test the second set
Acceptance Criteria for the V-2 Classification
A material is classified V-2 at the tested thickness when all of the following conditions are met:
- Afterflame time t1 or t2 for any individual specimen does not exceed 30 seconds
- The sum of afterflame times (t1 + t2) for all ten specimens does not exceed 250 seconds
- The combined afterflame and afterglow time (t2 + t3) for any specimen does not exceed 60 seconds
- Afterflame or afterglow of any specimen does not reach the holding clamp
- Flaming drips that ignite the cotton indicator are permitted, which is the characteristic that distinguishes V-2 from V-1
UL 94 and IEC 60695-11-10 also define controlled retest rules: when a single specimen shows a marginal result or only one specimen in a set fails specific numerical limits, an additional conditioned set may be tested to confirm or refute the classification, provided the overall afterflame totals remain within limits.
Applications
V-2 rated materials are widely specified across electrical and electronic product categories where moderate flammability performance is acceptable and where product safety standards do not mandate drip-free behavior:
- Enclosures and internal supports for information technology and audio/video equipment evaluated under IEC 62368-1, where V-2 materials may be used for parts located away from potential ignition sources
- Household appliance components covered by IEC 60335-1, including knobs, decorative trims, ducts, and non-live supporting parts
- Electrical installation accessories such as nylon cable ties, wiring clips, junction inserts, and conduit fittings, for which V-2 is the industry-standard minimum rating
- Connectors, terminal blocks, switch bodies, relay housings, and coil formers in low-voltage distribution and control equipment
- Fan blades, bearing mounts, and structural brackets in ventilation and cooling assemblies
- Battery pack housings, charger cases, and lighting component parts, subject to the specific requirements of the applicable end-product standard
- Automotive interior and non-safety electrical components, often tested alongside horizontal burn requirements such as FMVSS 302
Because product safety standards such as IEC 62368-1, IEC 60335-1, and IEC 60601-1 impose flammability requirements based on the proximity of materials to potential ignition sources and the mass of the part, manufacturers must verify that a V-2 rating satisfies the specific clause applicable to each component rather than assuming one rating suits all locations.
FAQ
What does a V-2 flame rating actually mean?
A V-2 rating means that when a vertical test bar is exposed twice to a small 50 W flame for 10 seconds each time, the material stops burning within 30 seconds per application, the total afterflame time for ten specimens stays below 250 seconds, and any flaming drops that fall may ignite the cotton indicator placed beneath the specimen. The material self-extinguishes reliably but is allowed to produce flaming drips.
How does V-2 differ from V-0 and V-1?
V-0 requires afterflame times of 10 seconds or less per application with no flaming drips. V-1 allows 30 seconds per application and a 250-second total, but still prohibits flaming drips. V-2 matches the extinguishing times of V-1 while permitting flaming drips, making it the least demanding of the three vertical small-flame classifications.
Which standards govern V-2 testing?
The primary standards are UL 94 (ANSI/UL 94) in North America and IEC 60695-11-10 internationally, together with its regional adoptions such as EN 60695-11-10 and GB/T 5169.16. The test apparatus and flame source requirements are defined in IEC 60695-11-4. Test reports from ISO/IEC 17025 accredited laboratories are accepted by certification bodies worldwide.
Is the V-2 rating thickness dependent?
Yes. Flammability classifications apply only at or above the thickness actually tested. A grade rated V-2 at 1.6 mm may perform worse at 0.8 mm, so products with thin-wall sections must verify the rating at the minimum wall thickness used in production, and part drawings often specify the minimum required flame rating together with the minimum thickness.
How many samples are needed for a V-2 test?
A minimum of two sets of five bar specimens (ten bars total) per thickness is required, each measuring 125 mm × 13 mm at the declared thickness. Laboratories typically recommend submitting additional spare specimens to cover retest scenarios under the UL 94 retest rules.
How long does V-2 testing take?
After the mandatory 48-hour conditioning period, the burn testing itself is completed within a few hours. Including sample preparation, test scheduling, and report issuance, typical turnaround at an accredited laboratory ranges from five to ten working days, longer if multiple thicknesses or retests are required.
Can a V-2 material replace a V-0 material in a product?
Not automatically. Product safety standards often require V-1 or V-0 for parts close to live connections, arcing components, or significant ignition sources, precisely because flaming drips are not acceptable in those positions. Any substitution must be validated against the flammability clauses of the applicable end-product standard and, where relevant, confirmed with the certification body.