Why are small changes in micron so important in determining the price of fine wool?

The price of wool of a specified micron is determined by supply and demand. It is hardly surprising that the price increases with decreasing micron, as the supply also decreases with decreasing micron.

However, it is not unusual to see a large step change in price for a change of 0.1 microns. When this occurs it is usually the result of mill specifications that demand that no lot within a consignment should exceed a specific micron value. If there are a number of orders for the same specification then this can dramatically increase competition between buyers, thereby driving up the price over very narrow range of variation.