This study investigated the mechanical behaviour of glass fibre epoxy composites with and without an embedded polyethylene terephthalate (PET) substrate used for printed electronic applications, with the mechanical behaviour integrity studied under different loading modes: three-point bending, tensile, and short-beam stress (SBS) tests. The main objective of this study was to investigate the influence of the substrate location within the laminate. Fracture profiles were observed by visual inspection during the mechanical tests and scanning electron microscopy (SEM) after failure to identify differences in the damage mechanisms and their propagation. Tensile tests indicated that embedding the PET substrate did not affect the ultimate strength of the laminate, while the bending and SBS tests indicated that the substrate integration reduced the bending strength and ILSS by 10% and 50%, respectively, depending on the substrate location.