Criteria HB V-2 V-1 V-0 5VB 5VA
Number of bar specimens as received 3 5 5 5 5 5
Number of plaque specimens as received         3 3
Number of ignitions 1 2 2 2 5 5
Maximum flaming time per specimen per flame application, sec   30 30 10    
Maximum total flaming time, 5 specimens, 2 ignitions, sec   250 250 50    
Specimen drips, ignites cotton   Yes No No No No
Maximum afterglow time, per specimen, sec   60 60 30    
Burn to holding clamp   NO NO NO NO NO
Maximum flaming or glowing combustion time after 5th flame application, sec         60 60
Maximum burning rate for specimens 3.0 mm to 13 mm thick over 75 mm span, mm/min 40          
Maximum burning rate for specimens less than 3.0 mm thick over 75 mm span, mm/min 75          
Plaque specimen exhibit burnthrough         Yes No

UL Test Descriptions

The number of seconds that a material resists the formation of a surface conducting path when subjected to a continuous arc of high voltage, low current characteristics.
The voltage which causes tracking on a material after 50 drops of 0.1% ammonium chloride solution has fallen on the surface of a specimen between two electrodes.
The number of arc rupture exposures (standardized as to electrode type and shape and electric circuit) which are necessary to ignite a material when they are applied at a standard rate, either on the surface of the material or at a specified distance from it.
The rate in mm/min that a tracking path can be produced on the surface of the material under standardized test conditions. Note is made if ignition of the material takes place.
The number of seconds needed to ignite standard specimens which are wrapped with resistance wire that dissipates a specified level of electrical energy.

Materials are investigated with respect to retention of certain critical properties (e.g., dielectric strength, flammability, impact strength, and tensile strength) as part of a long term thermal-aging program conducted in accordance with Underwriters Laboratories, Inc. Standard for Polymeric Materials-Long Term Property Evaluations (UL746B). The end-of-life of a material at each test temperature in this program has been assumed to be the time when the value of the critical property has decreased to 50% of its original (as received) value. The temperature index shown in the individual recognition correlates numerically with the temperature in degrees C above which the material is likely to degrade prematurely when based on a comparison with similar results on a material which has had acceptable service experience. More than one Relative Thermal Index may be appropriate for a given material depending on the property requirements for a given application.