Nanoparticle reinforced fibre composites promise enhanced product properties demanded for many fields of application. However, the targeted production of nanoparticle resin suspensions is demanding and requires detailed knowledge about the fundamental mechanisms acting during the process. In order to obtain this knowledge, the dispersing process of nanoparticle-suspensions with high viscosities is investigated by the example of epoxy resin alumina suspensions which are used as a matrix material for fiber reinforced plastics. The performance of several dispersing machines with differing stress mechanisms is compared and dependencies on process parameters are characterized. Laminar shear flow dispersing was performed in a three roller mill as well as in a kneader. In a pin-counter-pin stirred media mill and a basket mill dispersing between grinding media surfaces was investigated. The effect of process parameters on the stress energy/intensity and its effect on the product quality was studied for the respective stress mechanisms with special focus on the impact of suspension viscosity. An existing model to quantify the stress acting in laminar shear flow is extended to account for the influence of solids content utilizing the concept of shear stress equivalent shear rates. Deviations from commonly known dependencies of dispersing processes with grinding media are found and explained by a change in the governing stress mechanism which depends on the viscosity and particle size of the suspension. Process maps for the dispersing in highly viscous media are derived regarding desired particle size, energy efficiency and required solids content for the respective machines. (C) 2018 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.