Last updated: 2026-09-02 · 5 min read

What Does UL94 V-0 Mean — and How Does It Shape Your Resin Choice?

UL94 is the standard for flammability of plastic materials — V-0 is the most common self-extinguishing rating, meaning the material stops burning within 10 seconds on a vertical specimen — and achieving it shapes resin selection because most engineering resins in their natural state burn readily, requiring flame-retardant additives or specific polymer chemistries to pass. The rating is tested at specific thicknesses, so a V-0 rating at 1.5mm does not automatically transfer to 0.75mm — the resin must be qualified at the part’s actual wall.

Runner system — The channel network that delivers melt from the machine nozzle to each cavity. Cold runner: solidifies between shots, produces runner waste. Hot runner: stays molten, eliminates runner waste but adds $15k–$40k to mold cost. See also related guide.

Key Facts

  • UL94 has multiple ratings: HB (slow burning), V-2 (self-extinguishing, drips allowed), V-1 (self-extinguishing, no drips), V-0 (self-extinguishing, stops within 10 seconds), and 5V (more stringent than V-0).
  • The rating is thickness-dependent: a resin may be V-0 at 3.0mm but only V-1 or HB at 0.75mm — the datasheet must show the rating at the part’s actual wall thickness.
  • Flame-retardant additives affect processing: halogenated, phosphorus-based and mineral-filled systems each change melt flow, mechanical properties and molding parameters — the resin supplier’s processing guide is the baseline.

    • Runner system — The channel network that delivers melt from the machine nozzle to each cavity. Cold runner: solidifies between shots, produces runner waste. Hot runner: stays molten, eliminates runner waste but adds $15k–$40k to mold cost. The related guide covers adjacent topics.

    The UL94 Rating Scale

    Rating Behavior Typical Application
    HB Slow horizontal burning; not self-extinguishing Non-critical structural parts
    V-2 Self-extinguishing on vertical; dripping permitted Consumer electronics housings
    V-1 Self-extinguishing; no dripping Electrical enclosures
    V-0 Self-extinguishing within 10 seconds; no dripping Connectors, switches, appliance components
    5V More stringent than V-0; no specimen rupture High-risk electrical and transportation

    How Flame Retardants Change the Resin

  • Halogenated systems: effective at low loadings, but increasingly restricted by and — brominated and chlorinated additives face regulatory pressure.
  • Phosphorus-based: common in engineering resins like PC and PBT; good flame performance but can affect hydrolytic stability and color.
  • Mineral-filled: aluminum hydroxide or magnesium hydroxide release water when heated; high loadings (50-60%) impact mechanical properties and melt flow.
  • Each system changes processing: melt temperature, mold temperature, injection speed and packing pressure shift from the base resin — the supplier’s processing guide is the starting point, not the finish.

    • What the Datasheet Must Show

    A UL94-compliant resin datasheet lists the rating at specific thicknesses — typically 3.0mm, 1.5mm and 0.75mm — because flame performance degrades as walls thin. The part’s minimum wall must be covered by the rating; a V-0 at 3.0mm does not qualify a 0.75mm wall.
    The datasheet also names the specific grade, because flame-retardant packages vary within a resin family — one PC grade may be V-0 at 1.5mm while another is only V-2. Material selection starts with the flammability requirement, then narrows to grades qualified at the part’s wall, then considers mechanical properties and processability.

    Frequently Asked Questions

    Does the mold need to be different for flame-retardant resins?

    Not necessarily, but flame-retardant grades often have different flow characteristics — lower melt flow, higher viscosity — which may require larger gates, bigger runners or adjusted process parameters. The mold design should account for the specific FR grade’s rheology, not the base resin’s. Corrosive byproducts from some FR systems may also require corrosion-resistant steel or surface treatments.

    Can regrind be used with flame-retardant resins?

    Yes, but with tighter controls: regrind ratio is typically limited (10-15%) because flame-retardant additives can degrade with thermal history, and contaminated regrind introduces variability. The resin supplier specifies the maximum regrind percentage and the drying requirements — FR resins are often more moisture-sensitive than base grades.

    What if the part needs both UL94 and color?

    Color masterbatch must be compatible with the flame-retardant system — some pigments interact with FR additives and reduce flame performance. The resin supplier qualifies specific color concentrates with their FR grades; using unqualified colorants voids the flammability listing. The color masterbatch supplier provides compatibility documentation for the specific FR grade.

    Key Takeaways

    1. UL94 V-0 is the most common self-extinguishing rating; the rating is thickness-dependent, so the datasheet must show qualification at the part’s actual wall.
    2. Flame-retardant additives change processing — melt flow, mechanical properties and molding parameters shift from the base resin; the supplier’s guide is the baseline.
    3. Material selection starts with the flammability requirement, then narrows to grades qualified at the part’s wall, then considers mechanical properties and processability.

    Send aCatMould your UL94 requirement and the part’s minimum wall, and the material recommendation names grades qualified V-0 at that thickness — with the processing parameters, regrind limits and color compatibility documented, so the flame performance is a controlled property, not a datasheet hope.

    Sources
    Underwriters Laboratories — UL94 flammability standard
    Plastics Technology — flame-retardant resins and processing
    SPE — flammability and material selection guidance

    Sources: Plastics Technology · Plastics Technology Online · Society of Plastics Engineers (SPE) · ThomasNet