How Is UL94 5VA Achieved on PC/ABS? Wall Thickness and the Yellow Card System Explained

Vertical burning and 5V are two different tests

The UL94 vertical test (V-0 / V-1 / V-2) uses a 50 W flame applied twice for 10 seconds to a 125 mm × 13 mm bar, measuring afterflame time and whether drips ignite cotton. V-0 requires no single afterflame above 10 seconds and no more than 50 seconds total across five applications.

5VA / 5VB belong to a different part of the same standard: a 500 W flame applied five times for 5 seconds each, checking for burn-through. 5VA permits no burn-through; 5VB allows it but limits afterflame. Outdoor housings and EV charger enclosures frequently specify 5VA.

Wall thickness is the biggest variable

A single yellow card lists ratings by thickness tier, commonly 3.0, 2.0, 1.6, 1.0 and 0.8 mm. A material rated V-0 at 1.6 mm does not automatically pass at 0.8 mm — thin sections let heat through faster and molten drips detach sooner.

Always quote the thinnest actual wall of the finished part, not simply V-0.

Colour effects are underestimated

Carbon black generally improves flame performance, whereas certain organic pigments — phthalocyanines in particular — interfere with char formation or promote dripping, lowering the rating when the same formulation is recoloured.

The correct approach is to test each fee colour separately. If colour is not mentioned at quotation stage, natural or black is assumed.