A method of manufacturing an aerofoil blade includes the steps of providing: an aerofoil sub-assembly having a pair of aerofoil skins, wherein at least one of the skins is formed to have on its outer face an outer primary relief feature formed proud of the adjacent region of the outer face and an outer secondary relief feature projecting from the outer primary relief feature; arranging the aerofoil sub-assembly in a cavity die mould; and performing a hot forming process to form an internal cavity between the respective aerofoil skins by inflating the sub-assembly to conform the outer faces of the respective skins to the cavity die mould, whereby in conforming the respective outer faces of the skins to the cavity die mould, the outer primary and secondary relief features are transferred to the inner face of the respective skin to form respectively inner primary and secondary relief features.