What is a UL 94 flammability rating?

UL 94 classifies how plastic specimens behave in defined small-scale flame tests. It is material evidence under specified conditions, not proof that a finished enclosure is fireproof or approved for a particular product.

Is V-0 the highest UL 94 rating?

V-0 is the most demanding of the V-0/V-1/V-2 vertical classifications. UL 94 also includes different tests, including 5VA/5VB, HB, foam and thin-film classifications. These must not be treated as interchangeable approvals.

Which plastics meet V-0?

Select an exact manufacturer and grade with a current listing covering the colour and minimum thickness required. A polymer name such as ABS, PC/ABS, PPS or PEEK alone does not establish V-0 performance.

Does the rating depend on wall thickness?

Yes. Check the minimum thickness and colour recorded for the exact grade. A V-0 listing at 1.5 mm does not by itself demonstrate V-0 at 0.8 mm. Also assess the complete product under its applicable standard.

How much more does a flame-retardant grade cost?

There is no universal percentage. Compare current quotations for the exact grades, colour, quantity and documentation. Include density, part mass, processing and any additional verification in the comparison.

Does every batch need UL 94 testing?

Agree incoming checks, material traceability and any batch or finished-product testing with the responsible product-compliance specialist. A Yellow Card does not remove the need to control substitutions, colour, additives or recycled content.

UL 94 Flammability Ratings for Plastics: HB to 5VA Explained

Updated: 2026-10-22

UL 94 helps buyers specify the burning behaviour of plastics under controlled laboratory conditions. The useful purchasing question is which exact material listing and finished-product requirements apply to the proposed part.

What do the classes mean?

Classification	Selected acceptance criteria
HB	Horizontal burning rate or extinction before the relevant mark
V-0	Afterflame ≤10 s per application; no flaming particles igniting the cotton indicator
V-1	Afterflame ≤30 s per application; no flaming particles igniting the cotton indicator
V-2	Afterflame ≤30 s per application; flaming particles may ignite the cotton indicator
5VA	Separate 500 W test; afterflame plus afterglow ≤60 s after the fifth application, no flaming drips, no hole in the plaque
5VB	Same time and drip criteria as 5VA; a hole in the plaque is permitted

V-0 has stricter burning-time limits than V-1/V-2 within that test family. It is not the highest classification across every UL 94 method. VTM thin-film ratings are not equivalent to the corresponding V ratings. See UL's explanation of the test families. This overview is not the complete acceptance criteria or a test procedure.

Check the exact grade, thickness and colour

Use the manufacturer's full grade designation and current listing. Do not assume all ABS is HB, all PPS is V-0, or that adding a flame retardant establishes a rating. The effect on impact strength, electrical properties, ageing and processing must be checked in the candidate grade's documentation.

The UL Yellow Card programme records tested material properties. Check the relevant thickness and colour entry, recognition conditions and current status. A material card is evidence about that material, not a certificate for the finished enclosure. Changes to colourants, additives or recycled content need review against the applicable recognition conditions.

Specify the complete product requirement

Identify the applicable end-product standard and edition with the responsible compliance specialist. Agree the required material class, minimum wall, openings, heat sources, electrical clearances and any finished-product tests. There is no universal rule that every enclosure within 13 mm of live parts must use V-0.

UL 94 scope, section 1.4 makes final acceptance dependent on use in complete equipment. A material's laboratory classification must not be assumed to predict its end-use fire performance. UL 94 is not a general building-material fire rating.

Prepare a reviewable material request

State the product standard, required class and minimum wall at the relevant features.
Record the proposed manufacturer, exact grade, colour and material-card reference; mark an unselected grade as an open question.
Request traceability, substitution controls and the documentation or testing required before approval.
Compare dated quotations for the same quantity and scope. Include part mass, density, processing, documentation and verification costs; generic USD/kg tables or fixed FR premiums are not a project budget.

Collect these requirements in the RFQ brief and send the drawings for a project assessment. Material availability, documentation and production scope require project-specific confirmation.

Worked example: checking a proposed enclosure material

Consider an invented purchasing scenario, not a real UL listing or Nordmould project. The design has a nominal 1.8 mm outer wall and a local 0.8 mm section. A proposal describes a black grade as V-0 at 1.5 mm. That statement does not establish the required performance at the thinner feature, in a different colour or after an unlisted additive is introduced.

Create a requirement matrix with the actual drawing feature, required classification, minimum applicable thickness, grade/colour designation and current listing reference. Ask the responsible product-compliance specialist which features and test requirements govern the finished enclosure. Possible responses include selecting a properly documented grade, revising the geometry or agreeing additional assessment. None should be approved solely from the quotation's headline “V-0”.

The matrix should also identify open information. An unidentified colour concentrate is not equivalent to a confirmed colour entry, and a missing listing reference should remain unresolved. UL's colour-code reference helps interpret entries such as BK and ALL; verify the actual recognition conditions rather than assuming the abbreviation covers every formulation change.

What should change control cover after approval?

Keep the approved manufacturer's grade designation, colour, material-card reference and relevant drawing revision together. Agree who may authorise a supplier substitution, colourant change, recycled-content change or move to another production route. A similar family name and matching appearance do not establish that the replacement carries the same recognition.

Define the evidence needed at receipt and during production: material identity, lot traceability and records linking the approved material to delivered parts. Identify who investigates a document discrepancy and whether affected output must be held pending review. The required inspection or testing frequency comes from the applicable product requirements and agreed control plan, not a universal instruction to flame-test every batch.

Before release, review flammability alongside the other necessary characteristics: mechanical loading, service environment, electrical performance and assembly. A satisfactory flame classification does not make an unsuitable material appropriate for the product. UL's guide to reading a Yellow Card explains the wider material-property context; it does not replace the finished-product assessment.