Abstract: A method of depositing a heat reflecting coating on the inner surface of a tube comprises: introducing the tube into the second zone of a furnace having two temperature zones; injecting into the first zone a mixture of chemicals capable of reacting to form the coating material; simultaneously injecting into the first zone towards the second zone a plurality of jets of a carrier gas defining an annular array of jets around the first jet, and a further jet of a carrier gas also substantially parallel to the first jet but spaced closer thereto; controlling the temperature of the first zone to effect vaporization of the mixture in the first jet; and controlling the temperature of the second zone to effect the reaction of the vaporized materials of the mixture to form the coating material, and the deposition of the coating material on the surface of the tube in the second zone.