UL 746B relative temperature index test

Over the years many attempts have been made to provide some measure of the maximum service temperature which a material will be able to withstand without thermal degradation rendering it unfit for service. Quite clearly any figure will depend on the time the material is likely to be exposed to elevated temperatures. One assessment that is being increasingly quoted is the UL 746B Relative Temperature Index Test of the Underwriters Laboratories (previously known as the Continuous Use Temperature Rating or Index). 

The long-term, continuous-use temperature resistance ranges from about 120 to 125 °C, as measured by the UL 746B relative thermal index (RTI) test, which places its performance closer to that of the engineermg polymers such as polybutylene terephthalate (PBT), liquid crystal polymers (LCP), and polyethylene terephthalate (PET) than to that of performance polymers such as polyphenylene sulfide (PPS), polyether sulfone (PES), and polyamide imide (PAI). 

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