As part of an investigation into the causes of the harshness of certain wools, an apparatus was devised by means of which the ease or extent to which wool can be compressed is measured. Four samples of yarn differing in harshness have been tested with this apparatus. The same samples were also tested by a method described by Winson. The results show that when the wools are placed in order of decreasing harshness, they are also in order of increasing compressibility; the softer the wool the more easily it is compressed.Measurements have been made at 50% and at 60% relative humidity.