The most common environment used for Procedure A is the "Standard Laboratory Atmosphere". It is strictly defined as:
ASTM D618-21, titled "Standard Practice for Conditioning Plastics for Testing," provides the procedures for stabilizing plastic materials. Since polymers are sensitive to their environment, testing a "cold" sample versus a "warm" one can yield wildly different data. This standard eliminates those variables. Why Conditioning Matters astm d618-21 pdf
Plastics are hygroscopic and thermostatically sensitive. If you don't condition them: may fluctuate based on moisture content. Impact resistance can change with temperature shifts. Dimensional stability might fail due to thermal expansion. The most common environment used for Procedure A
Involves oven conditioning followed by desiccation to remove moisture. astm d618-21 pdf