Most polypropylene autosampler vial caps, including MicroSolv brand caps are designed for use at room temperature with a typical temperature range of 0°C to 60°C. It is best to stay within the specifications of the products for best results and safety.
Caution: An extreme temperature range of -55°C to 220°C is possible, however the silicone / PTFE septa will withstand a higher temperature but structural integrity of the polypropylene cap is lost.