UL 94 / IEC 60695-11

UL 94 Flammability Rating Selector

Check whether a UL 94 rating meets the class you need, and find the rating a plastic part typically requires from its role and governing standard - with the burn test behind each class and the thickness rule that trips people up.

Does a rating meet what you need?

Class you need

Class the material has

What class does my part need?

Part role / location

Governing standard

Min wall thickness

Method based on ANSI/UL 94 (Ed. 7, 2023; rev. Feb 2026) / IEC 60695-11-10 and -11-20 · reviewed June 2026 · method rev 1.0

How the ratings are tested

UL 94 burns a specimen horizontally (HB) or vertically (V and 5V), measuring how fast it burns, whether it self-extinguishes, and whether it drips. The ratings form a ladder from HB up to 5VA.

UL 94 ratings, least to most flame-resistant

The full ladder, with the burn test behind each class. A higher rating satisfies any lower requirement - but only at the thickness it was tested at.

Ratings are thickness-dependent and formulation-specific - always confirm against the UL Yellow Card at the part's minimum wall thickness.
Rating	Test	Self-extinguish	Drips
HB	Horizontal, 50 W (20 mm)	Burn rate limited; no self-extinguishing required	Not assessed
V-2	Vertical, 50 W (20 mm)	≤ 30 s after each flame application	Flaming drips allowed (may ignite cotton)
V-1	Vertical, 50 W (20 mm)	≤ 30 s after each flame application	No flaming drips
V-0	Vertical, 50 W (20 mm)	≤ 10 s after each flame application	No flaming drips
5VB	Vertical + plaque, 500 W (125 mm)	≤ 60 s after the 5th application	No drips; plaque may burn through
5VA	Vertical + plaque, 500 W (125 mm)	≤ 60 s after the 5th application	No drips; no plaque burn-through

How the ladder works

HB is a horizontal test - the bar only has to burn slower than a set rate, or stop before the 100 mm mark. It means slow-burning, not self-extinguishing, and is the lowest rating. The V ratings are vertical: once the flame is removed the specimen must self-extinguish, and the test also watches whether burning particles drip onto a cotton indicator below. V-2, V-1 and V-0 share the same idea and differ in how long flaming may persist and whether drips may be flaming.

The 5V ratings use a flame about five times more severe and add a plaque test. 5VB requires the bar to self-extinguish but allows a plaque to burn through; 5VA additionally forbids any burn-through, which makes it the highest class and the one called up for fire-enclosure-grade parts.

Why thickness changes everything

A UL 94 rating is tied to the thickness it was tested at, not to the resin in general. The same compound can be V-0 at 1.5 mm and only HB at 0.75 mm, because a thinner wall has less material to carry heat away and self-extinguish. That is why the binding value lives on the material's UL Yellow Card, listed per thickness, colour and formulation - and why you size the requirement to the part's minimum wall thickness, including thin ribs and bosses, not a thicker reference section.

What UL 94 does not tell you

UL 94 is a small-flame material screening test under controlled lab conditions. It says nothing about smoke density, gas toxicity, heat-release rate, or how a part behaves inside a real assembly fire, and a high rating does not by itself mean the finished product passes its safety standard. Glow-wire tests (common for appliances) and end-product fire tests cover the rest, so treat the UL 94 class as a necessary screen, not the whole fire-safety case.

Worked examples

Real calls an engineer makes - comparing a material to a requirement, and reading a requirement off a part's role.

Scenario	Result	Why
Need V-0; material is listed V-2 at 1.5 mm	Does not meet	V-2 is two steps below V-0 and allows flaming drips. Specify a higher class or a different resin.
Need V-1; material is V-0 at 0.8 mm	Meets (exceeds by 1)	V-0 outranks V-1 - valid here because the V-0 is listed at 0.8 mm, the part's wall thickness.
Internal bracket beside an SMPS, 62368-1	Target V-0	In or adjacent to a power source, so the customary minimum is V-0.
Battery case acting as its own fire enclosure	Target V-1	The fire enclosure wall itself is customarily V-1 minimum.
Combustible cable clip inside the fire enclosure	Target V-2	Major combustible parts inside a fire enclosure are typically V-2 minimum.

How UL 94 relates to other standards

Standard	Relationship	What it means
IEC 60695-11-10 and -11-20	Harmonized with	The IEC small-flame test methods that mirror the UL 94 horizontal-burn and vertical-burn procedures.
ISO 9772 and ISO 9773	Aligned with	The ISO equivalents for cellular (foam) materials and thin flexible materials.
IEC 62368-1 and UL 746C	Referenced by	End-product safety standards that call up a minimum UL 94 class for enclosure and part flammability.

This tool compares UL 94 classes and gives the customary requirement for a part's role. It is an engineering reference, not a compliance ruling - the binding minimum, the small-parts exceptions and the specimen rules live in your product standard, and the material's class lives on its UL Yellow Card at the actual wall thickness.

Where engineers use this

Enclosure and housing plastics

Confirming a candidate resin's flammability class meets the product safety standard at the part's real wall thickness, not a thicker reference bar.

Parts near live or arcing nodes

Deciding where V-0 is required versus where V-1 or HB is acceptable around power, connectors and ignition sources.

Material substitution reviews

Checking that a proposed alternate material still holds its rating before a second source is approved.

Frequently asked questions

Does a higher UL 94 rating always satisfy a lower requirement?

On the ladder, yes - a V-0 material meets a V-1, V-2 or HB requirement. The catch is thickness: the higher rating must be listed at your part's minimum wall thickness, and the 5V classes use a different specimen test from the V classes, so check the Yellow Card rather than assuming.

Is V-0 always better than V-2?

V-0 is more flame-resistant - it self-extinguishes faster and permits no flaming drips. But 'better' means meeting your standard's requirement: over-specifying adds cost and can hurt other properties such as impact strength or tracking resistance (CTI). Match the class to the requirement, not higher for its own sake.

What rating does a fire enclosure need?

Customarily V-1 for the enclosure wall itself, with combustible parts inside it usually required to be V-2; some equipment categories call for 5VB or 5VA. The binding minimum is set by your product standard for your construction - this tool gives the typical value plus the clause to verify.

Why does the same material show several different ratings?

Because ratings are assigned per thickness, colour and formulation, and the Yellow Card lists each combination. A resin can be V-0 at 1.5 mm and only HB at 0.75 mm, so a single 'V-0 material' claim is meaningless without the thickness it applies to.

Are 5VA and 5VB on the same scale as V-0?

They are more severe - a larger flame plus a plaque burn-through test - and sit above V-0, but they are a different test. A material rated 5V usually also carries a V rating for its thinner sections, so a 5VA part will typically satisfy a V-0 requirement too.

Does a UL 94 rating mean my product is fire-safe?

No. It is a material-level screening test; it says nothing about smoke, toxicity or heat-release rate, and it does not replace glow-wire or end-product fire testing. Treat it as one required screen within the product standard, not proof of compliance on its own.

Related tools and standards

UL 94 standard explainedWhat each rating means and the test behind it Creepage & clearance calculatorMaterial group (CTI) and spacing for the same insulation barrier IEC 62368-1 explainedThe hazard-based standard that calls up these ratings

Sources: UL 94, Standard for Tests for Flammability of Plastic Materials for Parts in Devices and Appliances · IEC 60695-11-10 and IEC 60695-11-20 (small-flame test methods). Verify against the current edition.