Specimens molded from the plastic material are oriented in either a horizontal depending on the specifications of the relevant test method, and they are subjected to a defined flame ignition source for a specified period of time.

 

UL 94 HB Rating

A material having a thickness between 3 and 13mm will be classified as a HB material if it does not have a burning rate exceeding 40mm per minute. For material with thickness less than 3mm the burning rate should not exceed 75mm per minute. The material will also be rated as HB if it ceases to burn before the 100mm mark independent of thickness.

 

UL 94 HBF: HBF, HF-1 and HF-2 - Horizontal Burning Foamed Material

This test grants three different types of ratings depending on burning rates and or afterflame times. A material will be classified as a HBF material if it does not have a burning rate exceeding 40mm per minute over a 100 mm span or if ceases to burn before flaming or glowing reach the 125mm mark.