The diameter range is very important in the processing and in the handle of the finished product. A fairly tight histogram indicates that the diameter of the fleece is uniformly consistent, and this makes the best yarn. The suggested range for cashmere down with a mean of 15 microns, is 8-24 microns, while for18 microns, the range is 12-28 microns. The standard deviation and coefficient of variation are two measures used to describe the spread of distribution. These terms are important to the breeder when assessing the distribution of the fibre he is producing.

The important point with distribution is that it must have a distinct cut-off. The distribution should be symmetrical so that it is a mirror-image of itself on each side of the mean. Problems during processing occur when the distribution of the down fibres is not succinct, but tends to "tail-off" towards the fibres with greater diameter. No matter what the mean diameter, the processors require fibre with a minimum of fibres over 27 microns.

Most of the problems with fibre distribution have been experienced in white crossbred fibre, Breeders need to identify the goats producing fibres which fall in the 28-40 micron range. They may be either coarse down, or in some cases, fine guard hair. While both present problems during processing, the fine guard hair is highly undesirable and impossible to remove. It is also important that none of the down fibres are modulated. When modulated fibres occur in this diameter range, they are most likely fine guard hairs.