Engineering Reference

UL 94 flammability rating

A standard test classifying how a plastic behaves when exposed to a flame.

Definition

The ratings run HB (horizontal burn, the weakest), V-2, V-1, V-0 (vertical, self-extinguishing, with V-0 the best) and 5VA/5VB for the most demanding applications.

The rating is thickness-dependent — a material rated V-0 at 3 mm may be only V-2 at 1.5 mm. Quote the thickness with the rating; a bare "V-0" is incomplete.

Common misuse

Quoting a UL 94 rating without its thickness. The same material can have different ratings at different wall thicknesses.

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