The short answer
UL 94 rates how a plastic burns in small-scale lab tests. From lowest to highest: HB (slow burn on a horizontal bar), V-2, V-1 and V-0 (vertical bars that must self-extinguish, with V-0 the fastest), then 5VB and 5VA (a larger flame applied five times). Every rating belongs to a specific grade at a stated thickness and color, as shown on its UL yellow card.
UL 94 is the flammability test most electrical and appliance specifications point to. It is a test of the material, run on molded bars and plaques. For choosing a flame-retardant grade for a part, see your part needs a flame rating.
UL 94 ratings at a glance
| Rating | Test orientation | Key criteria | Typical uses |
|---|---|---|---|
| HB | Horizontal bar | Burn rate ≤40 mm/min (3–13 mm thick) or ≤75 mm/min (under 3 mm), or flame stops before the 100 mm mark | Parts where the end-product standard asks for no more than HB |
| V-2 | Vertical bar | Each afterflame ≤30 s; total for 5 bars ≤250 s; flaming drips may ignite cotton | Some appliance and device internal parts |
| V-1 | Vertical bar | Each afterflame ≤30 s; total for 5 bars ≤250 s; no drips that ignite cotton | Housings and internal parts where V-1 is accepted |
| V-0 | Vertical bar | Each afterflame ≤10 s; total for 5 bars ≤50 s; no drips that ignite cotton | Connectors, terminal blocks, breakers, enclosures |
| 5VB | Vertical bar and horizontal plaque, 500 W flame | Burning and glow stop within 60 s after the 5th application; no drips that ignite cotton; plaque may burn through | Enclosures where the standard accepts 5VB |
| 5VA | Vertical bar and horizontal plaque, 500 W flame | As 5VB, and the plaque must not burn through | Enclosures where the end-product standard calls for 5VA |
A plain summary of the UL 94 criteria, not the full standard. Ratings apply only to the specific grade, thickness and colors on its yellow card; grades vary.
HB: horizontal burn
A bar about 125 × 13 mm is held horizontally and lit at one end with a small flame. It is marked at 25 mm and 100 mm from the lit end, and the burn rate is timed between the marks. The material rates HB if the burn rate is no more than 40 mm/min for bars 3–13 mm thick, no more than 75 mm/min for bars under 3 mm, or if the flame goes out before the 100 mm mark.
V-0, V-1 and V-2: vertical burn
A bar of the same size hangs vertically over a layer of dry cotton about 300 mm below. A 20 mm (50 W) flame is applied to the bottom for 10 seconds and removed; the afterflame time (t1) is recorded. As soon as it stops flaming, the flame is applied for another 10 seconds, and the second afterflame (t2) and afterglow (t3) are recorded. Two sets of five bars are tested, one conditioned at 23°C / 73°F and 50% relative humidity for 48 hours, the other aged 168 hours at 70°C / 158°F.
- V-0: each afterflame (t1 or t2) ≤10 s; total afterflame for the five bars ≤50 s; afterflame plus afterglow after the second application (t2 + t3) ≤30 s per bar; no drips that ignite the cotton; no burning up to the clamp.
- V-1: each afterflame ≤30 s; total ≤250 s; t2 + t3 ≤60 s; no drips that ignite the cotton; no burning to the clamp.
- V-2: the same time limits as V-1, but flaming drips that ignite the cotton are allowed.
5VA and 5VB: the 500 W test
The 5V tests use a flame about five times as severe as the V tests: a 500 W flame roughly 125 mm tall. It is applied to the specimen for 5 seconds, removed for 5 seconds, and repeated until it has been applied five times. Bars are tested vertically; 150 × 150 mm plaques are tested horizontally, with the flame aimed at the underside. For both ratings, flaming and glowing must stop within 60 seconds after the fifth application and drips must not ignite the cotton. 5VB allows the plaque to burn through (a hole); 5VA does not. 5V testing is run only on materials that already rate V-0 or V-1.
Thickness and color
A thin wall heats through and burns more easily than a thick one, so ratings are listed by thickness, for example V-0 at 1.5 mm and 5VA at 3.0 mm. Match the rating at your part's thinnest wall. Pigments and colorants can change burning behavior, so a listing names the colors it covers: all colors, natural and black only, or specific color numbers. A grade that is V-0 in natural is not automatically V-0 in a custom red.
The yellow card (UL Product iQ)
When UL recognizes a plastic grade, the result is published as a "yellow card" in UL's online directory, UL Product iQ for plastics. The card names the producer and the exact grade, and lists, by thickness and color, the UL 94 rating, the relative thermal index (RTI) and electrical values such as CTI and hot-wire ignition. A flame value on a data sheet or a producer's own test result is weaker evidence than a yellow card.
Material rating vs. product approval
A UL 94 rating describes how test bars of the resin behave. It does not approve your product. The finished product is evaluated under its own end-product standard, which sets the required rating and thickness and may add other tests. UL's rules for molders (UL 746D) also limit regrind and added color concentrate in a rated grade, and adding your own color can take a part outside the listing. See electrical and electronics resins and the best plastic for electrical housings.
Related tests often on the same spec
- Glow wire (IEC 60695-2-12 for GWFI, IEC 60695-2-13 for GWIT): a heated wire pressed into the material. Household appliance standards call for values such as GWFI 850°C / 1562°F and GWIT 775°C / 1427°F on some parts in unattended appliances. A V-0 rating does not guarantee a glow-wire result.
- RTI (UL 746B): a long-term thermal index for electrical and mechanical properties, listed by thickness. It says nothing about burning.
- CTI (comparative tracking index): resistance to surface electrical tracking, shown on yellow cards as a performance level category (PLC), where 0 is best.
How to check a grade's rating
- Get the requirement in writing: rating, thickness, color, and the end-product standard behind it.
- Find the exact grade name from the data sheet or bag label. See how to read a resin data sheet.
- Look up the yellow card in UL Product iQ for that grade.
- Read the row for your thickness and color. Confirm the rating holds at your thinnest wall.
- Check RTI, CTI and glow wire if your spec calls for them.
- Keep a copy with the part records; recheck it if the grade changes.
What to send us for a quote
- The rating, thickness and color you need, and any halogen-free requirement
- The grade you run now, or the part and resin family
- Quantity and ship-to city
We aim to send your quote within one to three business days.
Common questions
What is the difference between UL 94 V-0, V-1 and V-2?
All three are vertical burn tests. V-0 requires each bar to stop flaming within 10 seconds after each flame application; V-1 and V-2 allow 30 seconds. V-0 and V-1 do not allow drips that ignite the cotton below; V-2 does.
Is V-0 better than HB?
Yes. HB is the lowest UL 94 rating and only limits the burn rate of a horizontal bar. V-0 requires a vertical bar to self-extinguish quickly without flaming drips that ignite cotton.
What is the difference between 5VA and 5VB?
Both use a larger flame applied five times to bars and plaques, and burning and glowing must stop within 60 seconds with no drips that ignite the cotton. 5VB allows the flame to burn a hole through the plaque; 5VA does not.
Why does a UL 94 rating list a thickness?
Thin sections burn more readily than thick ones, so a grade can be V-0 at 3 mm and only V-2 at 1.5 mm. The rating applies at the listed thickness and is generally taken to cover thicker walls, not thinner ones.
What is a UL yellow card?
The summary of a plastic grade's UL recognition, searchable in UL's online directory (UL Product iQ). It lists the flame rating by thickness and color, along with RTI, CTI and other electrical values.
Does a V-0 resin make my product UL approved?
No. UL 94 rates the material. The finished product is evaluated under its own end-product standard, which decides what rating, thickness and other tests are required.
Is UL 94 the same as IEC 60695-11-10?
They are harmonized. IEC 60695-11-10 covers the 50 W horizontal and vertical tests and IEC 60695-11-20 covers the 500 W test, so the methods closely match UL 94, but a UL listing comes from UL's own program.
Tell us the rating you need
A polymer chemist reviews every request, then matches your grade or finds a qualified equivalent and prices it.
What to send for an accurate quote
- The grade name, from any supplier, or a data sheet
- Color (natural, black or a custom match)
- Fill type and percentage, if any
- Melt flow, if you know it
- Quantity for this order and what you use in a year
- Ship-to city and state or province