{ "id": "ep8pfvr1gy", "slug": "ul-94", "title": "UL 94", "updated": "2026-10-15", "topic_path": [ { "id": "technology", "label": "Technology and the built world", "api_url": "https://www.edgepedia.org/api/v1/topics/technology" }, { "id": "technology.engineering", "label": "Engineering and manufacturing", "api_url": "https://www.edgepedia.org/api/v1/topics/technology.engineering" }, { "id": "technology.engineering.manufacturing.metrology.quality", "label": "Metrology, quality, and inspection", "api_url": "https://www.edgepedia.org/api/v1/topics/technology.engineering.manufacturing.metrology.quality" } ], "geo": [ { "id": "geo.us.t1946.technology.engineering.manufacturing.metrology.quality", "label": "United States · 1946 to 2000: Metrology, quality, and inspection", "api_url": "https://www.edgepedia.org/api/v1/geo/geo.us.t1946.technology.engineering.manufacturing.metrology.quality", "path": [ { "id": "geo.us", "label": "United States", "api_url": "https://www.edgepedia.org/api/v1/geo/geo.us" }, { "id": "geo.us.t1946", "label": "United States · 1946 to 2000", "api_url": "https://www.edgepedia.org/api/v1/geo/geo.us.t1946" }, { "id": "geo.us.t1946.technology", "label": "Technology and the built world", "api_url": "https://www.edgepedia.org/api/v1/geo/geo.us.t1946.technology" }, { "id": "geo.us.t1946.technology.engineering", "label": "Engineering and manufacturing", "api_url": "https://www.edgepedia.org/api/v1/geo/geo.us.t1946.technology.engineering" }, { "id": "geo.us.t1946.technology.engineering.manufacturing.metrology.quality", "label": "Metrology, quality, and inspection", "api_url": "https://www.edgepedia.org/api/v1/geo/geo.us.t1946.technology.engineering.manufacturing.metrology.quality" } ] } ], "excerpt": "UL 94 is a UL standard for flammability of plastic materials, classifying polymers by small-scale flame tests into ratings such as V-0, V-1, and HB.", "snippet": "UL 94 is a UL standard for flammability of plastic materials, classifying polymers by small-scale flame tests into ratings such as V-0, V-1, and HB.", "node": "technology.engineering.manufacturing.metrology.quality", "markdown": "# UL 94\n\nUL 94 is the Standard for Safety of Flammability of Plastic Materials for Parts in Devices and Appliances, published by UL. It classifies polymeric materials by how they burn in small-scale flame tests, and its stated purpose is only a preliminary indication of a material's acceptability for a particular application, not a verdict on the finished product.[1](https://shopulstandards.com/ProductDetail.aspx?UniqueKey=44036)\n\n| Key fact | Detail |\n|---|---|\n| Classes | 12 classifications: 5VA, 5VB, V-0, V-1, V-2, HB for enclosure and structural plastics; HF-1, HF-2, HBF for foams; VTM-0, VTM-1, VTM-2 for thin films[2](https://www.ul.com/services/combustion-fire-tests-plastics) |\n| V-series flame | 20 mm (50 W) flame applied twice for 10 s each[2](https://www.ul.com/services/combustion-fire-tests-plastics) |\n| V-0 limits | Each specimen burns ≤10 s after either application, total ≤50 s per set, afterglow ≤30 s, no flaming drips[3](https://mm.digikey.com/Volume0/opasdata/d220001/medias/docus/402/UL_Test_Procedure.pdf) |\n| Thickness limits | Tests not applicable above 13.0 mm thickness or 1 m² surface area[1](https://shopulstandards.com/ProductDetail.aspx?UniqueKey=44036) |\n| Conditioning | Two regimes: 48 h at 23 °C/50% RH, and 168 h (7 days) at 70 °C[3](https://mm.digikey.com/Volume0/opasdata/d220001/medias/docus/402/UL_Test_Procedure.pdf) • [7](https://gasketfab.com/wp-content/uploads/2025/09/Unlocking-the-Mystery-of-UL94.pdf) |\n| 5V flame | 500 W, 125 mm flame, about five times more severe than the V/HB flame[2](https://www.ul.com/services/combustion-fire-tests-plastics) |\n| Rating validity | Tied to the tested thickness, color, and formulation; verify on the UL Product iQ Yellow Card[6](https://passive-components.eu/flammability-ul94-and-what-it-means/) |\n\n## What UL 94 is and what it measures\n\nThe standard covers flammability tests of polymeric materials used for parts in devices and appliances. Its tests are small-scale Bunsen-burner procedures performed on standardized bars and plaques, and the standard states plainly that the performance level determined by these methods shall not be assumed to correlate with performance in end-use application, which depends on size, form, and end-use. Final acceptance of a material depends on its use in complete equipment that conforms with the standards applicable to that equipment.[1](https://shopulstandards.com/ProductDetail.aspx?UniqueKey=44036)\n\nThe scope has hard boundaries. With one exception (the Radiant Panel Index Test), the tests do not apply to parts thicker than 13.0 mm or with a surface area over 1 m², they do not cover building construction materials, and they do not evaluate fire resistance, flame spread, smoke, or heat release rate.[1](https://shopulstandards.com/ProductDetail.aspx?UniqueKey=44036) A V-0 rating also does not mean a material is \"self-extinguishing\", nor that flame-retardant additives are present; it means the V-0 test criteria were met.[4](https://fire.tc.faa.gov/2013Conference/files/Test_Method_and_Analysis_I/BuonicontiBunsenBurner/BuonicontiULflammabilityPres.pdf)\n\n## Test apparatus and procedure\n\n**Vertical V-series test.** Ten specimens per thickness, each a 125 mm x 13 mm bar, are tested in two sets of five: one set preconditioned 48 hours at 23 °C and 50% relative humidity, the other conditioned 7 days at 70 °C.[3](https://mm.digikey.com/Volume0/opasdata/d220001/medias/docus/402/UL_Test_Procedure.pdf) • [4](https://fire.tc.faa.gov/2013Conference/files/Test_Method_and_Analysis_I/BuonicontiBunsenBurner/BuonicontiULflammabilityPres.pdf) Each bar is suspended above a bed of dry absorbent surgical cotton placed 12 inches below. A roughly 20 mm burner flame is applied for 10 s and, if burning ceases within 30 s, re-applied for a second 10 s. Afterflame time after each application and afterglow time after the second are recorded, and the cotton is inspected for ignition by flaming drips.[3](https://mm.digikey.com/Volume0/opasdata/d220001/medias/docus/402/UL_Test_Procedure.pdf) • [5](https://www.sciencedirect.com/science/article/abs/pii/S0010218020304806)\n\n**5V test.** Bar specimens receive five 5-second applications of a 5-inch (125 mm), 500 W burner flame angled 20° from vertical, with five specimens per thickness in each conditioning regime.[3](https://mm.digikey.com/Volume0/opasdata/d220001/medias/docus/402/UL_Test_Procedure.pdf)\n\n**HB test.** Horizontal specimens 5\" x 12\" x thickness are conditioned 48 h at 23 °C/50% RH and exposed to a single 30 s flame application.[3](https://mm.digikey.com/Volume0/opasdata/d220001/medias/docus/402/UL_Test_Procedure.pdf)\n\n## The classifications\n\n**V-0, V-1 and V-2** come from the same vertical test and differ in time limits and drip behavior:[2](https://www.ul.com/services/combustion-fire-tests-plastics)\n\n| Class | Individual afterflame | Total (set) | Afterglow after 2nd flame | Flaming drips ignite cotton? |\n|---|---|---|---|---|\n| V-0 | ≤10 s | ≤50 s (10 flame applications) | ≤30 s | No |\n| V-1 | ≤30 s | ≤250 s | — | No |\n| V-2 | ≤30 s | ≤250 s | — | Yes, allowed |\n\nThe cotton indicator is what separates V-1 from V-2: if the flame ceases within the time limits but flaming particles or drops fall and ignite the cotton, the material is classed V-2.[4](https://fire.tc.faa.gov/2013Conference/files/Test_Method_and_Analysis_I/BuonicontiBunsenBurner/BuonicontiULflammabilityPres.pdf) • [5](https://www.sciencedirect.com/science/article/abs/pii/S0010218020304806) Materials that fail the vertical test receive NR or are evaluated in the horizontal configuration as HB.[5](https://www.sciencedirect.com/science/article/abs/pii/S0010218020304806)\n\n**HB** is a horizontal burn test with a single 30 s flame application. The burning rate must not exceed 40 mm/min (1.5 in/min over a 3.0\" span) for specimens 3–13 mm thick, or 75 mm/min (3.0 in/min) for specimens under 3 mm (0.120\"); alternatively the flame must cease before the 4.0\" mark.[2](https://www.ul.com/services/combustion-fire-tests-plastics) • [3](https://mm.digikey.com/Volume0/opasdata/d220001/medias/docus/402/UL_Test_Procedure.pdf)\n\n**5VA and 5VB** come from the 500 W test, an ignition source approximately five times more severe than the V-0/V-1/V-2 and HB flame. No specimen may flame more than 60 s after the fifth flame application or drip flaming particles that ignite the cotton. Specimens with no burn-through hole earn 5VA; a rating of 5VB is assigned when burn-through occurs but the other criteria are met.[2](https://www.ul.com/services/combustion-fire-tests-plastics) • [3](https://mm.digikey.com/Volume0/opasdata/d220001/medias/docus/402/UL_Test_Procedure.pdf)\n\nTwo further families exist. HBF, HF-1, and HF-2 apply to foams, and VTM-0, VTM-1, and VTM-2 to thin materials tested in a different vertical thin-film configuration; a VTM-0 rating cannot be considered equivalent to V-0 because the test methods are quite different.[2](https://www.ul.com/services/combustion-fire-tests-plastics)\n\n## By the numbers\n\nThe threshold quantities that decide a classification:[2](https://www.ul.com/services/combustion-fire-tests-plastics) • [3](https://mm.digikey.com/Volume0/opasdata/d220001/medias/docus/402/UL_Test_Procedure.pdf)\n\n- 10 specimens per thickness, two sets of five, in two conditioning regimes (48 h at 23 °C/50% RH; 7 days at 70 °C).\n- V-test flame: about 20 mm, applied 10 s, twice.\n- V-0: 10 s individual / 50 s total; V-1 and V-2: 30 s individual / 250 s total.\n- HB: single 30 s application, 40 mm/min (3–13 mm) or 75 mm/min (under 3 mm).\n- 5V: five 5-second applications of a 125 mm flame; 60 s maximum afterflame after the fifth.\n\n## Why thickness and geometry change the rating\n\nA UL 94 classification is always tied to the minimum tested thickness, and the rating applies at that thickness and above. The same compound can be V-0 at 1.5 mm and only HB at 0.75 mm;[8](https://standardclarity.com/calculators/ul-94-rating-selector/) another source gives the same general effect as V-0 at 1.5 mm falling to V-1 or V-2 at 0.8 mm.[6](https://passive-components.eu/flammability-ul94-and-what-it-means/) The sources agree on the mechanism but differ on how far a rating drops at thin walls, so designers should rely on the Yellow Card entries for the exact wall thickness rather than assuming any particular fallback class.\n\nThe mechanism is thermal: a thicker specimen requires more time and heat exposure to reach its ignition temperature, while in a thinner sample heat rapidly permeates and the polymer can degrade faster than the flame retardant can activate.[9](https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=910107) Common reported thicknesses for flame-retardant plastics in electronic enclosures are 1.6 mm and 3.2 mm.[9](https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=910107)\n\nA V-0 datasheet class does not prove a finished product passes. These are material classifications measured on standard bars and plaques, not statements about finished products; the same material can behave differently once molded thin, perforated for ventilation, or placed next to a heat source.[10](https://ulmeka.com/knowledge/iec-60695-fire-hazard-flammability-testing-overview) For high-temperature polymers such as PEEK, which decomposes around 600 °C and forms about 50% char residue, researchers have argued the UL-94 classification itself is inadequate.[11](https://onlinelibrary.wiley.com/doi/10.1002/fam.1100)\n\n## How ratings are certified and maintained\n\nVerification runs through UL Product iQ (iq.ulprospector.com): the official electronic Yellow Card lists the classification at every tested thickness, together with color coverage and formulation. Third-party lab reports, however well done, are not official recognition.[6](https://passive-components.eu/flammability-ul94-and-what-it-means/) • [7](https://gasketfab.com/wp-content/uploads/2025/09/Unlocking-the-Mystery-of-UL94.pdf)\n\nUL uses bracketing methods and fingerprints formulations during evaluation. Materials are listed at specific thicknesses and in specific colors, and some colors, red for example, are known to perform worse in the test.[4](https://fire.tc.faa.gov/2013Conference/files/Test_Method_and_Analysis_I/BuonicontiBunsenBurner/BuonicontiULflammabilityPres.pdf) • [7](https://gasketfab.com/wp-content/uploads/2025/09/Unlocking-the-Mystery-of-UL94.pdf) Colorants, additives, fillers, recycled content, or other formulation changes may fall outside the evaluated recognition, and sharing the same base polymer does not transfer a classification from one grade to another. Procurement documents should match the supplier, grade, color coverage, and thickness of the actual part rather than attach an unrelated V-0 certificate.[12](https://viox.com/ul-94-v-0-v-1-v-2-classifications-guide/)\n\n## How UL 94 compares with other flammability tests\n\nInternationally, IEC 60695-11-10 uses the same 50 W flame for HB and V-0/V-1/V-2, and IEC 60695-11-20 uses the 500 W flame for 5VA/5VB, so the same class designations appear on datasheets worldwide.[10](https://ulmeka.com/knowledge/iec-60695-fire-hazard-flammability-testing-overview)\n\nThe European complement is the glow-wire family. Glow-wire tests simulate thermal stress from overheated components such as overloaded resistors, at temperatures of 550, 650, 750, 850, or 960 °C depending on the specification; the end-product test (IEC 60695-2-11) is performed on the finished product, while GWFI (60695-2-12) and GWIT (60695-2-13) are material properties, GWIT commonly expressed as a temperature 25–30 K above the highest temperature at which the material does not ignite.[10](https://ulmeka.com/knowledge/iec-60695-fire-hazard-flammability-testing-overview) • [13](https://www.crepim.com/DOCS_CLIENT/Cable-Electric%20contactors-relay-Low%20tension%20directive-spread%20of%20flamme-ignitability-Glow%20wire%20test%20EN%2060695-2-10%E2%80%93Limit%20Oxygen%20Index-LOI%20ISO%204589%202-UL%2094%20VO%20V1%20V2.pdf) The 4th Edition of IEC 60335-1 made glow-wire tests mandatory for plastic components near electrical connections, requiring GWIT 775 °C or GWFI above 750 °C with surrounding components rated UL 94 V-1 or better.[14](https://plastanalisi.com/lab-deep-dive/2026/flammability-compliance-ul-94-v0-vs-glow-wire-gwfi-gwit/) Testing differs in burden as well: V-0 testing takes roughly 2-3 days with 10 specimens per thickness, while glow-wire characterization takes 5-10 days and over 30 specimens per temperature point.[14](https://plastanalisi.com/lab-deep-dive/2026/flammability-compliance-ul-94-v0-vs-glow-wire-gwfi-gwit/) Limiting Oxygen Index is a different measure entirely, the minimum oxygen concentration supporting combustion, of interest above 21%, the oxygen content of air.[13](https://www.crepim.com/DOCS_CLIENT/Cable-Electric%20contactors-relay-Low%20tension%20directive-spread%20of%20flamme-ignitability-Glow%20wire%20test%20EN%2060695-2-10%E2%80%93Limit%20Oxygen%20Index-LOI%20ISO%204589%202-UL%2094%20VO%20V1%20V2.pdf)\n\n## References\n\n1. UL 94 | UL Standards & Engagement — https://shopulstandards.com/ProductDetail.aspx?UniqueKey=44036\n2. Combustion (Fire) Tests for Plastics | UL — https://www.ul.com/services/combustion-fire-tests-plastics\n3. Specifications - UL Test Procedures (DigiKey-hosted) — https://mm.digikey.com/Volume0/opasdata/d220001/medias/docus/402/UL_Test_Procedure.pdf\n4. UL94 Small Scale Flammability (FAA Fire Test conference) — https://fire.tc.faa.gov/2013Conference/files/Test_Method_and_Analysis_I/BuonicontiBunsenBurner/BuonicontiULflammabilityPres.pdf\n5. Experimental characterization and modeling of the UL-94V test (Combustion and Flame) — https://www.sciencedirect.com/science/article/abs/pii/S0010218020304806\n6. Flammability of Polymer Materials and UL94 Explained — https://passive-components.eu/flammability-ul94-and-what-it-means/\n7. Unlocking the Mystery of UL 94 Flame Ratings (The Gasket Fabricator) — https://gasketfab.com/wp-content/uploads/2025/09/Unlocking-the-Mystery-of-UL94.pdf\n8. UL 94 Flammability Rating Selector - Standard Clarity — https://standardclarity.com/calculators/ul-94-rating-selector/\n9. Cone calorimeter analysis of UL-94 V-rated plastics (NIST) — https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=910107\n10. IEC 60695 Fire-Hazard Testing Overview — https://ulmeka.com/knowledge/iec-60695-fire-hazard-flammability-testing-overview\n11. PEEK polymer flammability and the inadequacy of the UL-94 classification (Fire and Materials) — https://onlinelibrary.wiley.com/doi/10.1002/fam.1100\n12. UL 94 V-0 vs V-1 vs V-2: Ratings and Test Criteria — https://viox.com/ul-94-v-0-v-1-v-2-classifications-guide/\n13. Fire regulation for E&E (Crepim) — https://www.crepim.com/DOCS_CLIENT/Cable-Electric%20contactors-relay-Low%20tension%20directive-spread%20of%20flamme-ignitability-Glow%20wire%20test%20EN%2060695-2-10%E2%80%93Limit%20Oxygen%20Index-LOI%20ISO%204589%202-UL%2094%20VO%20V1%20V2.pdf\n14. Flammability Compliance: UL-94 V0 vs. Glow Wire (GWFI/GWIT) — https://plastanalisi.com/lab-deep-dive/2026/flammability-compliance-ul-94-v0-vs-glow-wire-gwfi-gwit/\n\n---\n*Topic: Encyclopedia › Technology and the built world › Engineering and manufacturing › Metrology, quality, and inspection*\n\n*Initially written Sep 17, 2026 · Edited: Oct 11, 2026; Oct 15, 2026*\n\n*Copyright 2026 EdgeChat AI, a subsidiary of Biostate AI.*\n\nLicense: Edgepedia Community License 1.0, https://www.edgepedia.org/edgepedia/license\n", "same_as": [], "url": "https://www.edgepedia.org/ul-94", "markdown_url": "https://www.edgepedia.org/ul-94.md", "license": { "name": "Edgepedia Community License 1.0", "url": "https://www.edgepedia.org/edgepedia/license", "summary": "Free with credit, commercial use included. AI training is open to everyone. For other uses, organizations over USD 100M in revenue or 100M monthly users license separately.", "spdx": "LicenseRef-Edgepedia-Community-1.0" }, "credit": "\"UL 94\", Edgepedia (EdgeChat), https://www.edgepedia.org/ul-94. Edgepedia Community License 1.0.", "credit_md": "\"[UL 94](https://www.edgepedia.org/ul-94)\", Edgepedia (EdgeChat), [https://www.edgepedia.org/ul-94](https://www.edgepedia.org/ul-94). [Edgepedia Community License 1.0](https://www.edgepedia.org/edgepedia/license).", "credit_html": "\"UL 94\", Edgepedia (EdgeChat), https://www.edgepedia.org/ul-94. Edgepedia Community License 1.0.", "speakable": "UL 94 is a UL standard for flammability of plastic materials, classifying polymers by small-scale flame tests into ratings such as V-0, V-1, and HB." }