The Relative Temperature Index (RTI) according to standard UL 746 B is a measure of the thermal aging of polymers.
The thermal endurance of a material can be determined by measuring the changes in its mechanical and electrical properties in relation to a predetermined level.
The evaluation of the RTI is based on the Arrhenius equation which is used for aging processes. When all test temperatures have decreased to 50 % of the initial value (at the latest after 10,000 hours), the RTI value is extrapolated to 100,000 hours (Control + Candidate). The main properties which are evaluated in this test include:
> Dielectric strength
> Tensile strength