The micrometer (or micron) is a unit of length equalling one millionth of a meter (0.000039 inch). The symbol µm is used to indicate a micron. Microns are the standard measurement used for grading wool. Any wool finer than 25 µm can be used for garments, while coarser wools are used for rugs, carpets, etc. To put it in perspective, a human hair ranges from 17 to 181 µm.

The grid below shows the fiber diameters of the most popular of natural fibers. The smaller the diameter, the softer the fiber is to the touch, rendering them the most luxurious and therefore generally the most expensive. While cashmere is often thought to be the softest of natural fibers, the grid below shows that there are a number of other fibers far softer than the finest Pashmina Kashmir. Hover over each image to see fiber name and size.