The failure behaviour of fibreglass sandwich panels with structured internal cores (z-cored panels) was studied in bending. A finite element model was developed for the simulation of three point bending tests and this has been validated against experimental results. The model was able to predict both the elastic response and, more importantly, the failure behaviour of the structure. It is therefore suitable for use in the optimising the design of z-core sandwich panels for transport applications. The same modelling approach was also applied to the structural behaviour of a larger sandwich panel with a metallic insert which was employed in the design of a semitrailer as part of a demonstration of the viability of the technology. © 2007 Institute of Materials, Minerals and Mining.