Abstract: A method of producing a composite material in which a reinforcing material (eg as fibres) is embedded in a matrix material is characterized in that the reinforcement material comprises a polymer material having a draw ratio of at least 12:1 which is plama treated, prior to incorporation in the matrix, preferably to produce pitting in its surface whereby improved adhesion is obtained between the reinforcement material and the matrix material by mechanical interlocking of the pitted surface of the reinforcement material and the complementary surface of the matrix material. Preferably, the surface pitting is effected by a plasma discharge treatment. Preferably the average pit size is from 0.1 to 4 microns.