What Is a UL 94?

UL 94 is the UL standard for testing the flammability of plastic materials used in parts for devices and appliances. It rates how a small molded specimen burns after a controlled flame is applied, from HB (slow horizontal burning) through V-2, V-1 and V-0 up to 5VB and 5VA, the most flame-resistant.

In short: a UL 94 rating tells you whether a plastic keeps burning, drips flaming material or self-extinguishes, measured on a small lab specimen.

What Does a UL 94 Flammability Rating Mean?

UL 94, the Standard for Tests for Flammability of Plastic Materials for Parts in Devices and Appliances, uses small-scale tests under controlled laboratory conditions. Six of its classifications apply to the plastics used for enclosures, structural parts and insulators: 5VA, 5VB, V-0, V-1, V-2 and HB, listed from most to least flame-resistant. Separate classes cover low-density foams (HF-1, HF-2, HBF) and thin films (VTM-0, VTM-1, VTM-2). A VTM rating is not equivalent to the V rating with the same number.

In the HB test a horizontal specimen must burn slower than a set rate. In the V tests a vertical specimen is flamed twice and must self-extinguish within set times, and the rating records whether flaming drips ignite a cotton indicator below. The 5V tests use a flame roughly five times more severe, applied up to five times.

UL 94 is a material rating, not a product certification. It is a preselection test that helps equipment makers choose plastics. UL notes that building codes do not accept UL 94 in place of their own large-scale fire tests. Results from most UL 94 tests also do not apply to material thicker than 13 mm (0.5 in).

UL 94 Ratings Compared: HB, V-2, V-1, V-0, 5VB, 5VA

Rating	Test setup	Key pass criteria	Flaming drips that ignite cotton
HB	Horizontal; 20 mm (0.8 in) flame for 30 s	Burning rate ≤ 40 mm/min (1.6 in/min) at 3–13 mm thick, ≤ 75 mm/min (3.0 in/min) under 3 mm, or flame out before the first mark	Not assessed
V-2	Vertical; 20 mm, 50 W flame, 2 × 10 s	Each burn ≤ 30 s; total ≤ 250 s across 10 flame applications; afterflame + afterglow ≤ 60 s	Allowed
V-1	As V-2	Each burn ≤ 30 s; total ≤ 250 s; afterflame + afterglow ≤ 60 s	Not allowed
V-0	As V-2	Each burn ≤ 10 s; total ≤ 50 s; afterflame + afterglow ≤ 30 s	Not allowed
5VB	Vertical; 125 mm, 500 W flame, 5 applications	Burning + afterglow ≤ 60 s after the fifth application; a burn-through hole is allowed	Not allowed
5VA	As 5VB	As 5VB, and no burn-through hole	Not allowed

For all V ratings, no specimen may burn up to the holding clamp.

How to Specify UL 94 for a Plastic Part

• Put the rating in the drawing or RFQ. Write the class and the resin grade, for example "UL 94 V-0 grade," rather than just "flame retardant."
• Check the thickness. Ratings are earned on specimens of a given thickness, and even the HB criteria change with thickness. Confirm that the grade's rating covers your part's thinnest wall.
• Treat it as one input. The end product may need its own certification; a V-0 material does not make the finished device compliant by itself.
• Keep the paper trail. Request material certifications that tie the molded lot to the specified grade.

At NICE Rapid, CMM reports and material certifications are available on request, and plastic injection molding orders carry material traceability and batch records.

Frequently Asked Questions

What is UL 94?

UL 94 is the UL standard for testing the flammability of plastic materials used for parts in devices and appliances. It classifies materials as HB, V-2, V-1, V-0, 5VB or 5VA based on how small specimens burn after a controlled flame is applied.

What does UL 94 V-0 mean?

V-0 means vertical specimens stopped burning within 10 seconds after each of two 10-second flame applications, with no more than 50 seconds of total burning across 10 flame applications, and no flaming drips igniting the cotton below.

Is a UL 94 flammability rating the same as product certification?

No. UL 94 rates the plastic material on small lab specimens. It helps designers choose materials, but the finished product may still need its own evaluation, and building codes do not accept UL 94 in place of their fire tests.

Related Services at NICE Rapid

• Plastic Injection Molding — ABS, PC, nylon and other engineering plastics, with material traceability and batch records on every order.
• Compression Molding — glass-reinforced BMC and SMC parts for electrical enclosures and switch components.
• Request a Quote — include the required UL 94 class and resin grade in your RFQ so it is reviewed with your quote.

Sources

1. UL Solutions, "Combustion (Fire) Tests for Plastics" — the 12 UL 94 classifications and their groupings; HB, V and 5V test criteria (flame sizes, application times, burning times, dripping, hole formation, HB burning rates by thickness); 5V flame about five times more severe; VTM not equivalent to V — ul.com
2. UL, "Understanding UL 94 Certifications and Limitations" (The Code Authority newsletter) — full title and scope of UL 94; small-scale tests; not applicable to material thicker than 13.0 mm; model codes do not recognize UL 94 ratings in lieu of code-required fire tests — code-authorities.ul.com