A core for a composite structure is described. The core has first and second core layers, and an interlayer region between the first and second core layers. At least one of the first and second core layers has hinge portions that facilitate draping of the core without interrupting the interlayer region. The interlayer region may include functionality such as a radar reflecting layer and/or optical fibres. Alternatively, the core may be a bonded core in which the interlayer region includes an adhesive layer for bonding the first and second core layers together.