A round sample of 144 cm² is kept for at least 15 hours in a hermetically sealed exsiccator (capacity about 2 l) at 37 °C and 50% relative humidity. In the process, the humidity is adjusted by means of a magnesium nitrate solution (about 100 ml).
Under these conditions, at least 5 (preferably 7) test persons evaluate the intensity of the odour perceived by briefly opening the exsiccator. The intensity of the odour is given marks by means of a grade scale ranging from 1 (no odour) to 5 (ver y strong odour). When a test person has stated his or her decision, the exsiccator shall be closed again and be kept under the conditions specified above for at least another 30 minutes.