A prepreg comprising a structural layer of packed unidirectional conductive fibres comprising thermosetting resin in the interstices, and a first outer layer of resin comprising thermosetting resin, and being essentially free of unidirectional conductive fibres, which when cured under elevated temperature, produces a cured composite material comprising a cured structural layer of packed unidirectional conductive fibres and a first outer layer of cured resin comprising unidirectional conductive fibres dispersed within.