UL 94

UL 94 - Flammability Ratings for Plastics

Standard for Tests for Flammability of Plastic Materials for Parts in Devices and Appliances

Maintained byGiorgi Gaprindashvili PublishedFebruary 7, 2026 UpdatedJuly 19, 2026

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.

Key facts

Full title: Standard for Tests for Flammability of Plastic Materials for Parts in Devices and Appliances
Published by: UL (Underwriters Laboratories)
Harmonized with: IEC 60695-11-10 / -11-20, ISO 9772 and ISO 9773
Common ratings: 5VA, 5VB, V-0, V-1, V-2, HB (plus foam HBF/HF-1/HF-2 and thin-film VTM-0/1/2)
What it measures: Small-flame ignitability and self-extinguishing behaviour only
Verify on: The material's UL Yellow Card, at the actual wall thickness

Horizontal vs vertical burn

HB is a horizontal test: the bar must 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 and 5V ratings are vertical, where the sample must self-extinguish after the flame is removed - a far more demanding condition that also looks at whether the material drips burning particles onto a cotton indicator below.

The 5V tests use a flame roughly five times more severe and add a plaque test: 5VA must not burn through, while 5VB may form a hole.

Choosing a rating

The right rating is set by the end-product standard - IEC 62368-1 for AV/IT equipment, IEC 60601-1 for medical, IEC 60335-1 for appliances - not picked from a datasheet. Parts in or next to current-carrying or heat-generating assemblies usually need V-0 or better; enclosures and structural parts in some categories need 5VA or 5VB; external non-structural parts may only need HB. A higher rating than the standard requires adds cost and can hurt other properties such as impact strength or tracking resistance (CTI).

What UL 94 does not tell you

It is a material-level screening test under controlled lab conditions. It says nothing about smoke density, gas toxicity, heat-release rate or how the part behaves in a real assembly fire, and a high UL 94 rating does not by itself mean the finished product meets its safety standard. Glow-wire and end-product fire tests cover the rest.

UL 94 ratings, least to most flame-resistant

Ratings are thickness-dependent and formulation-specific - always confirm against the UL Yellow Card at the part's minimum wall thickness.
Rating	Orientation	Self-extinguish	Drips
HB	Horizontal	Slow burn (no self-extinguish required)	-
V-2	Vertical	≤ 30 s	Flaming drips allowed
V-1	Vertical	≤ 30 s	No flaming drips
V-0	Vertical	≤ 10 s	No flaming drips
5VB	Vertical + plaque	≤ 60 s	No drips; plaque may burn through
5VA	Vertical + plaque	≤ 60 s	No drips; no burn-through (highest)

Tools that use this standard

UL 94 rating selector Creepage & clearance calculator Enclosure & Safety Standards

Related 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.

Frequently asked questions

What is the difference between UL 94 V-0 and V-1?

Both are vertical-bar ratings from the same test; V-0 is the stricter pass. For V-0 each specimen must self-extinguish within 10 seconds after each of two flame applications, the total afterflame time for the set must not exceed 50 seconds, afterglow must not exceed 30 seconds, and no flaming drips may ignite the cotton indicator below. V-1 relaxes the times to 30 seconds per application and 250 seconds total, with afterglow up to 60 seconds, and still allows no cotton-igniting drips.

What is the difference between V-1 and V-2?

The burn-time limits are the same. The only difference is dripping: V-2 permits flaming particles that ignite the cotton indicator beneath the specimen, while V-1 does not. A V-2 material can self-extinguish just as quickly as V-1 but is allowed to shed burning drips.

Is V-0 the highest UL 94 rating?

No. Within the vertical-bar (V) series V-0 is the top, but the 5V series is more demanding. The 5V test uses a larger flame applied five times and adds a burn-through check on plaques: 5VB permits a hole (burn-through) while 5VA permits none. 5VA is the most stringent UL 94 classification.

What does the HB rating mean?

HB is the lowest classification and comes from the horizontal burn test, not a self-extinguishing one. It means the material burns slowly enough to stay under a maximum linear burn-rate limit, or stops before a reference mark. Unlike the V ratings, HB does not require the material to self-extinguish once the flame is removed.

Does a UL 94 rating apply at any thickness?

No. A rating is tied to the specific wall thickness, colour and formulation tested. A resin rated V-0 at 1.5 mm may not hold V-0 at 0.8 mm, and a formulation change such as a new colorant can invalidate a prior rating. Always confirm the rating on the material's UL Yellow Card at your actual wall thickness.

Does a UL 94 rating mean a material is fireproof or safe?

No. UL 94 is a small-flame screening test on a standard specimen under laboratory conditions. It classifies ignitability and self-extinguishing behaviour only; it does not measure toxicity, smoke, heat release, behaviour in a real fire, or whether the finished product is safe. The governing product standard decides which rating a given part needs.

Which UL 94 rating do I need for my part?

UL 94 does not set that; the end-product safety standard does, for example IEC or UL 62368-1 for information and audio/video equipment. Those standards specify the required class by the part's function and location, so start from the product standard and then choose a material whose Yellow Card meets it at your thickness.

Source: UL Standards & Engagement. An overview for design reference - verify against the current edition before relying on it for compliance.