The effect of different impact events, which occur in fine grinding mills, on the development of the physical properties of dry Norway spruce wood in pulverisation was studied. Dry Norway spruce wood with a median size d(50) = 199 mu m (+/- 6 mu m) was pulverised in an opposed jet mill and an oscillatory ball mill down to a d(50) of approximately 20 mu m. In addition, knowledge from an earlier study was used to obtain information about high-speed rotor impact milling. The development of physical properties, such as aspect ratio, width of its distribution and cellulose crystallinity, as a function of particle size was significantly different using oscillatory ball milling compared to using jet milling. When pulverising to median sizes of approximately 20 mu m, oscillatory ball milling resulted in lower cellulose crystallinity and rounder, more uniform particle shapes than did jet and rotor impact milling. It is proposed that media mills are capable of imposing higher energies and, consequently, cause stronger physical changes for dry Norway spruce wood particles compared to impact-based non-media mills. (C) 2013 Elsevier B.V. All rights reserved.