Mixtures of aluminium particles and glass fibres are compounded, granulated and shaped by powder injection moulding (PIM). At each of these steps the fibres accumulate damage, resulting in significantly shorter lengths in the moulded product when compared with the initial formulation. Data are collected using the same combined solids loading (65 vol.- particles plus fibres) in experiments consisting of three binders and three ratios of powder to fibre. A model for fibre damage is presented based on fracture concepts, showing the longest fibres fail preferentially. This leads to a cascade of fracture events, where damage accumulates in the largest fibres, which can be described by breakage theory. The resulting fibre length distribution follows a lognormal distribution, as confirmed by statistical tests using the experimental data. The model confirms the progressive reduction in fibre length during the PIM process where the fibres in the moulded product are about 10-15 of the initial size. © 2006 Institute of Materials, Minerals and Mining.