Compared to other engineering plastics, Ryton® PPS compounds exhibit a superior combination of both long-term and short-term thermal stability. The chart shown below compares the thermal stability of various engineering plastics using a plot of Heat Deflection Temperature (HDT) vs UL Relative Temperature Index (RTI). The HDT is a measure of short-term thermal stability in terms of maintaining dimensional integrity at elevated temperatures. It indicates the temperature at which a plastic material will no longer maintain its shape under an applied load (in this case 264 psi or 1.8 MPa). The UL RTI is a measure of long-term thermal stability in terms of resistance of the polymer to thermal degradation. It indicates the temperature at which a plastic material will retain at least 50% of its original mechanical strength after 100,000 hours, and is typically considered to be the maximum continuous use temperature of the material. The high HDT of Ryton® PPS compounds (>500°F, >260°C) demonstrates their ability to be used in applications requiring high temperature cycling, and to withstand IR soldering temperatures and other PC board soldering methods for Surface Mount Technology (SMT). With UL RTIs of 200°C to 240°C (392°F to 464°F), Ryton® PPS compounds will hold up better than other engineering plastics in applications requiring extensive exposure to high temperatures.