An apparatus useful in treating a carbon fibre precursor material under predetermined conditions of temperature and gaseous environment. The apparatus includes a housing, and a reaction chamber disposed within the housing. The reaction chamber is elongate and has an entry port at a first end and an exit port at a second end. The entry and exit ports are configured to allow passage of a carbon fibre precursor material into and out of the reaction chamber respectively. A heater or heating system is configured to heat a wall of the reaction chamber. In use, a precursor material is passed through the reaction chamber and is thereby heated.