Pre-test conditioning
Preparation of plastics for characterization and testing

Pre-test conditioning, the last step before the actual measurements, often involves equilibration with an atmosphere of specified temperature and humidity, generally 23°C and 50% RH (relative humidity) for "room temperature" tests. However, other conditions may be specified, with slight differences in temperature, while humidity conditions may be omitted for polymers that are not very sensitive to humidity.

For tests at higher or lower temperatures, the standards generally specify the temperature and time conditioning conditions. It's important to remember that polymers are poor thermal conductors, so core temperatures can differ significantly from surface temperatures. Similarly, moisture penetrates only slowly, and equilibrium is generally only reached after a few days, or even longer for certain polymers. Obviously, the greater the thickness, the longer it takes...