The Thermal Stability Test is designed to insure that dimensional changes in carbonated PET bottles will not be excessive during their expected lifetime. This is also known as a “creep” test.
Representative bottles are measured under “as-received” non-carbonated conditions. Bottles are then carbonated and placed in an environmental room at 37.8°C ± 2.5° (100°F ± 5°) and 85% ± 10% humidity for 24 hours. After this time, bottles are removed from the room and re-measured (final measurements). These final measurements must be completed within 4 hours of removal from the environmental chamber and must be made at the same locations as the initial measurements. A comparison is then made between the “as-received” and the final measurements.