Vapour-grown carbon fibres are very promising as composite reinforcers due to their low cost, about $ 10/kg. They are currently produced on a laboratory scale, but to reach an industrial production volume, it would be necessary to increase their final length up to the centimetre ran ge. Current literature describes how the catalytic growth of such short fibres is finally poisoned by the carbon-deposition pyrolytic process, so the achievement of fibres larger than a very few millimetres, is rather difficult. A slight change in the habitual routine production process, however, it makes possible to grow this type of fibre by an as-vapour-liquid-solid growth model, which yields grown fibres with a very attractive length. In this model, hydrogen plays an important role.