A system for measuring glass transition temperature of a polymer can include a cell having a closed bottom and a peripheral wall extending from the bottom, a sample holder having a first supporting pin and a second supporting pin spaced apart from the first supporting pin, a loading probe in the cell for selectively contacting a polymer sample disposed on the sample holder, a temperature probe in the cell, a heater in the cell, a temperature sensor, a source of pressure, a source of gas in communication with the cell, and a data acquisition system operably connected to the loading probe, the temperature probe and the source of pressure. The first and second supporting pins and the loading probe in the cell provide a three-point flexural bending assembly for measuring bending of the polymer sample under varied conditions of temperature and pressure in the presence of a gas.