Abstract: A method of forming a hollow spar for an aerofoil includes forming a sandwich structure having a first structural layer, a second structural layer and a cellular core layer located in between the first structural layer and the second structural layer. At least part of the sandwich structure is removed at intervals corresponding to one or more corner locations, and the sandwich structure is folded at the one or more corner locations to define a hollow space and form the spar. A chordwise extending rib section for an aerofoil has a substantially planar web with a chordwise length; and a reinforcement strip attached to an edge of the web over substantially the majority of the chordwise length.