Methods of improving the toughness of the bond between a foam core and a carbon fibre face-sheet in a sandwich structure were investigated. The Single Cantilever Beam (SCB) on a travelling platform was identified as an appropriate mode-I dominant test-method. The introduction of machined grooves in the foam resulted in a 50% improvement in the measured toughness of the face-sheet-core bond. Toughening of the face-sheets via core–shell rubber particles resulted in a change in fracture locus away from the interface and into the foam. The use of aramid fibre-reinforced foam as the core of the sandwich was also found to improve the interface bond toughness by up to 50%. The fibre-reinforced foams promoted the emergence of R-curve behaviour as the crack propagated.