If a part goes into an electrical enclosure, appliance or building product, a customer or code may require a flame rating. Picking the right flame-retardant (FR) resin means matching the rating, the thickness and sometimes the color.
UL 94 ratings in plain English
| Rating | What it means |
|---|---|
| HB | Burns slowly on a horizontal bar. The lowest rating. |
| V-2 | Self-extinguishes on a vertical bar; flaming drips allowed. |
| V-1 | Self-extinguishes; no flaming drips; longer burn time allowed than V-0. |
| V-0 | Self-extinguishes quickly; no flaming drips. The most common requirement. |
| 5VA / 5VB | Tougher test with a larger flame, for enclosures. |
Three things buyers miss
- Ratings are tied to thickness. A grade rated V-0 at 3 mm may only be V-2 at 1.5 mm. Match the rating at your thinnest wall.
- Ratings can be tied to color. Check that your color is covered by the listing.
- Check the actual listing. UL’s online database (the “yellow card”) shows each grade’s rating by thickness and color, plus its thermal index.
Common FR resin options
- FR polycarbonate and FR PC/ABS: enclosures and housings.
- FR ABS and FR HIPS: lower-cost housings.
- FR nylon and FR PBT: connectors, terminal blocks, breakers.
- FR polypropylene: appliance parts.
- Halogen-free FR grades, where customers or regulations require them.
Replacing an FR grade
If you need an equivalent, it has to carry its own listing at your thickness and color, and your end-product approval may need updating. Plan that into the timeline. Replacing a grade →