Abstract: Filamentous substrates are coated with diamond by a chemical vapor deposition process. The substrate may then be etched away to form a diamond filament, such as a diamond tube or a diamond fiber. In a preferred embodiment, the substrate is copper-coated graphite. The copper initially passivates the graphite, permitting diamond nucleation thereon. As deposition continues, the copper-coated graphite is etched away by the active hydrogen used in the deposition process. As a result a substrate-less diamond fiber is formed. Diamond-coated and diamond filaments are useful as reinforcement materials for composites, is filtration media in chemical and purification processes, in biomedical applications as probes and medicinal dispensers, and in such esoteric areas as chaff media for jamming RF frequencies.