Abstract: A fire resistant plastic structure comprises a pair of parallel walls, wherein the spacing between the walls is filled with an array of mutually spaced strut elements, thereby providing a flow path for a cooling fluid throughout the spacing.

Abstract: A stiffener for a panel (40) comprises a fibre/composite box section reinforcement member (42) having a floor (44) laminated to the panel (40) and integrally to the walls of the box which in turn extend outwardly and are laminated to regions of the panel alongside the member (42). The stiffener may comprise several reinforcement members joined together and may further have a further layer of material applied across the top of the members (42) to provide a generally even top surface. A method of forming the stiffeners in glass fibre/resin composite is also disclosed.