Method and apparatus are described for making e.g. panels by thermoforming outer films (20, 21) to a cellular core (5). The core is formed in a first step by corrugating and moulding together two thermoplastics sheets (12, 13), and then the films (20, 21) bonded in a press (26). The panel (28) produced may be suitable for use as a door A plurality of cores may be formed in series or in parallel and united to form a multilayer core, which may provide for a range of functions including water and electrical services and heat transfer