A process for producing a thermoformable fibre-plastics composite product comprising lignolcellulosic or natural fibres, particularly but not exclusively useful as an intermediate product in subsequent manufacture, comprises conveying the fibres in a dry or wet air stream and applying to the fibres a thermoplastic binding agent, and forming the fibres into a solid or semi-solid product such as a panel, which is thermoformable. In at least a preferred embodiment the process may be carried out in known plant for manufacture of medium density fibre board.