The confined particle bed comminution of fine materials is of huge economic importance for comminution technology and, therefore, also of fundamental interest for comminution science. This paper presents some experimental results on energy absorption, compression, increase of fineness and energy efficiency proving the effect of stress velocity for compressive stresses at different stress intensities (pressures) and for the two materials limestone and quartz. Our results show that an increasing stress velocity leads to a higher energy absorption in the particle bed, but also to lower compression, comminution and energy efficiency. These effects are not only explained by friction but also by flow losses for which a flow model is presented. (C) 2007 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.