UL 94 uses different small-scale test methods for HB, V and 5V classifications. The classifications describe material behavior under those controlled tests; they do not by themselves establish an end-product requirement.
Key facts
Full title
Standard for Tests for Flammability of Plastic Materials for Parts in Devices and Appliances
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-burning classification. The V-0, V-1 and V-2 classifications use a vertical specimen and distinguish afterflame/afterglow behaviour and whether flaming particles ignite the cotton indicator. These are defined test outcomes, not a complete prediction of real-product fire behaviour.
UL Solutions describes the ignition source used for 5VA/5VB as approximately five times more severe than the source used for the V and HB tests. The 5V method also includes a plaque hole-formation criterion: 5VA does not permit a hole, while 5VB does. Treat that as a distinction between defined test methods, not as a mathematical severity multiplier or a universal ranking across every UL 94 family.
Choosing a rating
The required flammability classification comes from the applicable end-product standard and construction, not from UL 94 alone. Use the product-standard clause to identify the relevant material test family and requirement, then verify the exact material listing at the thickness, colour/formulation and other conditions that apply to the part.
Do not infer a product-level pass merely because one material classification appears more demanding than another. Foam and thin-film classifications use different test methods, and even within the common molded-material group the end-product standard decides what evidence is acceptable for the particular part.
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.
Common molded-material UL 94 classifications and test distinctions
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 hole formation in the plaque test
This table summarizes the common HB, V and 5V material-test classifications only. It is not a universal hierarchy for every UL 94 family. Ratings are thickness- and formulation-dependent; verify the material's actual UL record at the conditions used in the product.
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?
V-0 is the most demanding classification within the V-0/V-1/V-2 vertical-bar method. UL 94 also includes the separate 5VA/5VB method, which uses a different ignition source and adds plaque hole-formation criteria; UL Solutions describes that ignition source as approximately five times more severe than the one used for the V and HB tests. That does not turn every UL 94 classification, including foam and thin-film families, into one interchangeable ranking. The governing end-product requirement determines which test family and classification matter.
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 alone does not determine that. Start with the applicable end-product standard and the part's function, construction and location. Then verify a material listing that satisfies the required test family/classification at the actual thickness and other listed conditions. A class shown in a datasheet is not by itself a product-compliance determination.