To transfer extremely high mechanical loads into multi-layer fibre-reinforced plastics (FRP), it is often necessary to design structural components as thick-walled composites. In the DFG research project PAK988 "DIWA", through a synergetic combination of in-situ process monitoring, structure analysis and material tests with accompanying numerical simulations, new evaluation criteria as well as process control strategies will be developed. Therefore, in order to gain a deeper understanding of the factors influencing the failure mechanisms of thick-walled composites, this paper describes an experimental study that examines the effect of specimen size on the compressive, tensile and flexural properties of bi-axially braided glass fibre/polyurethane composites.