Large variations in the felting rate of loose wool are attributed, principally, to crimp characteristics of the single fibers.Crimp form alone accounts for 77.4% of the variation and, in combination with the directional frictional effect, for 83.3%.Crimp frequency accounts for 32.5% of the variations and, in combination with diameter, for 70.4%. The product of these latter two variables also accounts for a considerable amount of variation (67.1%).