In this contribution, the influence of the particle aspect ratio on mechanical properties of composites is investigated. As example, copper-polyvinyl butyral (PVB) composites are studied. Copper particles in two different sizes, 29.5 mu m and 260 mu m, are coated in a spouted bed with PVB and the produced granules are then directly pressed to a bulk material or they are firstly rolled, to increase the aspect ratio, and then pressed. For the bulk material the mechanical properties, such as Young's modulus, strength, strain and fracture toughness, are determined. The results show that elongation at break, strength and fracture toughness increase with increasing aspect ratio. For the coarser particles, the bending strength could be doubled at 72 vol. % of copper. The maximal increase for the toughness in the composites with fine particles is about 65 vol. %. In the composites with coarser particles the maximal increase is even 80 vol. %. The fracture toughness increases with increasing crack length due to effects inside of the composites. The optimal composition is between 72 and 75 vol. % of copper. (c) 2018 Elsevier B.V. All rights reserved.