[Home](/)/[Resources](/resources)/UL 94 Flammability Testing USSafetyRegulation guide # UL 94 Flammability Testing for Plastic Components UL 94 — the Standard for Tests for Flammability of Plastic Materials for Parts in Devices and Appliances — is one of the most frequently referenced material qualification standards in electronics product safety. A UL 94 rating on a plastic component is not a product certification — it is a material property rating. Understanding what UL 94 ratings mean, when they are required, and how they interact with product-level safety standards is essential for hardware product development. Copy Link[Share on WhatsApp](https://wa.me/?text=https%3A%2F%2Fkrono-labs.com%2Fguides%2Ful-94-flammability-testing) At a glance Standard UL 94 Ratings (low to high) HB → V-2 → V-1 → V-0 → 5VA Database UL QMFZ2 (Yellow Card) Common product standard UL 62368-1 Rating type Material property (not product cert) ## UL 94 ratings explained ### HB — Horizontal Burn (Least Restrictive) HB is the lowest UL 94 rating. The specimen is oriented horizontally and the flame must extinguish before reaching a marked point, or burn at a rate below 76 mm/min for materials thicker than 3 mm (38 mm/min for thinner). HB is suitable for low-risk enclosure housings where fire spread is the concern, not ignition resistance. Most consumer electronics enclosures use HB-rated material at minimum. ### V-2 — Vertical Burn, Dripping Allowed V-2 specimens are oriented vertically and must extinguish within 30 seconds after each of two 10-second flame applications. Flaming drips are permitted. V-2 is used for components where self-extinguishing behaviour is needed but flaming particle release is acceptable given the product's risk profile. Less common than V-0 in modern electronics designs. ### V-1 — Vertical Burn, No Flaming Drips V-1 has the same 30-second afterflame requirement as V-2 but prohibits flaming or glowing drips that ignite indicator cotton placed below the specimen. V-1 is required where dripping particles could propagate fire to other materials — relevant for components positioned above other flammable parts in an enclosure. ### V-0 — Most Restrictive Vertical Rating V-0 specimens must extinguish within 10 seconds after each flame application (total afterflame for all specimens in a set cannot exceed 50 seconds), with no flaming drips. V-0 is typically required for internal structural components, connectors, wire insulation, and components near high-power circuits in UL 62368-1 and similar product safety standards. ### 5VA / 5VB — Severe Flame Test 5VA and 5VB ratings use a more severe flame (500W) applied five times for 5 seconds each. 5VA prohibits burn-through of the specimen; 5VB permits burn-through. These ratings are required for large enclosures and housings of high-power equipment where a 500W flame represents a realistic fire scenario. 5VA is the most stringent UL 94 rating. ## When UL 94 ratings are required UL 94 ratings are required whenever a product must comply with a safety standard that references flammability requirements for plastic materials. The specific rating required depends on the component's location within the product, proximity to heat sources, and the applicable product standard. 01 UL 62368-1 (Audio/Video, IT, and Communications Equipment — the replacement for UL 60950-1) requires specific flammability ratings for enclosures, internal structural parts, and components adjacent to heat sources — typically V-1 or V-0 depending on component location and power level. 02 IEC 60950-1 and its successor IEC 62368-1 (harmonised international versions) reference equivalent flame test requirements aligned with UL 94, making these ratings relevant for CE marking as well as UL certification. 03 UL 508A (Industrial Control Panels) specifies enclosure flammability requirements for industrial electrical equipment enclosures, typically requiring V-0 or 5VA/5VB for the panel housing. 04 UL 94 for PCB substrate — FR4 (the standard glass-epoxy PCB material per IPC-4101) is typically rated 94V-0 or 94V-1 at standard thicknesses. PCB flammability is evaluated as part of UL 62368-1 product certification. 05 Fire-rated enclosures for battery products — lithium battery packs and energy storage systems require enclosure materials with higher flame resistance ratings to limit fire propagation in thermal runaway scenarios, often 5VA. ## Testing process and material qualification ### UL QMFZ2 Yellow Card Database UL maintains the QMFZ2 database (the 'Yellow Card' system) listing all UL-recognized plastic materials and their ratings at tested thicknesses and colours. Before specifying a plastic material for a product, engineers should verify the material appears in QMFZ2 at the required rating and at the thickness used in the actual design. Specifying a material without a Yellow Card for the required rating creates a gap in product safety evidence. ### Thickness-Dependent Ratings UL 94 ratings are always tied to the specific thickness at which a material was tested. A material rated V-0 at 3.0 mm may only achieve HB at 1.5 mm. The Yellow Card lists tested thicknesses, and designers must verify the rating at the thinnest cross-section of the moulded part — not the nominal wall thickness. Thin ribs, bosses, and snap-fit features are common failure points. ### Colour Variants and Separate Testing Colour pigments and additives can affect flammability — a natural (uncoloured) V-0 material may not retain its V-0 rating when colour pigments are added. UL requires separate testing for each colour variant. The Yellow Card will list approved colours. Using an off-Yellow-Card colour in a moulded part invalidates the V-0 rating for product certification purposes. ### Regrind and Recycled Material Requirements Using regrind or recycled plastic — even regrind of the same base material — requires re-qualification testing. Regrind may have altered molecular weight, different contamination levels, or changed additive profiles that affect flammability performance. Product safety standards generally require that regrind be tested and qualified to the same rating as virgin material if it is used in safety-critical components. ## Common mistakes in UL 94 compliance ### Using HB-Rated Enclosure Where V-0 Is Required The most common UL 94 compliance error. Engineers select an HB-rated plastic for an enclosure housing because it meets the minimum material requirement, without checking that the product safety standard (e.g., UL 62368-1) requires a higher rating for the specific component location. A product built with HB enclosure plastic that should be V-0 will fail the product certification evaluation. ### Assuming Product-Level Marking Covers Component Ratings A UL Listed or CE-marked complete product does not mean every plastic component within it is independently V-0 rated. The product-level certification verifies that the combination of materials meets the standard's requirements at the system level — but component substitution during manufacturing without re-evaluation can invalidate this. Each safety-relevant plastic part must be traceable to a Yellow Card entry. ### Not Verifying Thickness at Thinnest Cross-Section Engineers frequently specify the nominal wall thickness when checking the Yellow Card, but the relevant thickness for UL 94 is the minimum thickness anywhere in the part. Thin features — ribs, snap-fits, living hinges, grill openings — are regularly thinner than the nominal wall and may not be covered by the V-0 rating at the nominal thickness. Minimum section thickness must be measured and verified. ### Substituting Materials Without Re-Qualification Mid-production material substitutions — switching to a different grade, supplier, or colour of plastic — require re-evaluation of the UL 94 rating even if the new material appears similar. The product's safety file must be updated with the new Yellow Card reference. Failing to do this is a common cause of product safety audit findings and can trigger re-certification of the product. ## Frequently asked questions ### Is a UL 94 V-0 rating on a plastic material the same as a UL Listed product? No. A UL 94 V-0 rating is a material property rating issued to the material manufacturer — it confirms the plastic itself meets the V-0 flammability criteria at the tested thickness and colour. A UL Listed product is a system-level certification that the complete product meets the applicable product safety standard. UL 94 V-0 rated materials are an input to the product certification — a necessary but not sufficient condition for a UL Listed product. ### What UL 94 rating does FR4 PCB substrate need to meet? FR4 PCB substrate (glass-epoxy laminate per IPC-4101) is typically UL 94 V-0 rated at standard thicknesses (1.6 mm and above) and appears in the UL QMFZ2 database under multiple material designations from laminate manufacturers. UL 62368-1 and IEC 62368-1 require V-0 rated PCB substrate for most electronics applications. Very thin PCBs (below approximately 0.5 mm) may have different ratings — verify the Yellow Card for the specific laminate and thickness used. ### How do we verify UL 94 ratings for components sourced from Chinese manufacturers? Verify through the UL QMFZ2 online database, which is publicly searchable. Enter the material trade name, manufacturer, and grade to find the Yellow Card entry. If the material does not appear in QMFZ2, it has not been UL-recognized and its V-0 claim cannot be verified for product safety purposes. For product certifications to UL standards, safety evaluators require Yellow Card evidence — self-declared V-0 ratings from a material supplier without a QMFZ2 entry are not accepted. ### Does a UL 94 V-0 material rating expire? UL 94 material ratings in the QMFZ2 database are maintained as long as the material manufacturer continues their UL Follow-Up Services programme. UL conducts periodic factory inspections and tests to verify continued compliance. If a manufacturer discontinues the programme, the Yellow Card listing is removed or marked inactive. Engineers should verify that the Yellow Card for a specified material remains active before finalising a design, particularly for products with long production runs. **Disclaimer:** This page is an educational resource only and does not constitute legal or regulatory advice. UL 94 requirements vary by product standard, application, and jurisdiction. Always consult the applicable product safety standard and a qualified safety engineer for component-specific flammability decisions. 🇺🇸 US roadmap for your product Every standard, document, and test that applies — free, no account required. See your free roadmap[ Want an expert to take your product through 🇺🇸 US compliance for you? One consultant from Krono's compliance team takes your product from requirements to legal sale, with a fixed quote before any work starts. See compliance services](/services) Learn this properly In-depth course that teaches the full process, not just this one answer. [Start the course — $149](/courses/07-ul-certification-complete-guide)[Prefer to read? 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