Investigations into the processes of grinding and classification are presented. It is shown how the properties of filled polymer products like powder coatings or toner can be tailored through grinding and classification. A systematic approach to describe the process by a machine and a material function is introduced. Single particle comminution tests allow the determination of the material function. The breakage probability curves of different organic and inorganic materials can be transferred to one single master curve. The transfer of single particle tests to production mills seems to be possible, at least for the given example that of powder coatings. This comparison shows that the width of the final size distribution is determined in this example by the material function and not by the operation of the mill. Significant improvements were achieved for both powder quality, i.e. the amount of fines below 10 mum, and the yield by employing two new classifiers for the removal of fines. The classifiers were operated inline, directly after a classifying mill.