2.1 The conditioning atmosphere should have a
temperature of 20 ± 20°C and relative humidity of 65 ±
2%.
2.2 The specimen should be laid flat, in the conditioning
atmosphere for a period of 24 hours, or for a sufficiently longer
period in order to ensure that the mass of the specimen shows no progressive
change greater than 0.25% when it is determined at intervals of 2
hours.