Abstract: A curable prepreg comprising a structural layer of unidirectional electrically conductive fibres having interstices therebetween, having a first outer face and an essentially parallel second outer face, and comprising thermosetting resin impregnated within the structural layer and present within the interstices, and a first layer of thermosetting resin in contact with the first outer face of the structural layer, wherein the ratio of the electrical conductivity in the x-direction, parallel to the conductive fibres, to the electrical conductivity in the y-direction perpendicular to the conductive fibres, is less than 1000.