n An advanced reinforcing fiber produced by passing 10-µm, resistively heated tungsten wire through an atmosphere of boron trichloride and hydrogen. Hydrogen reduces the BC13 and the boron deposits on the wire to make a filament from 120 to 140 µm in diameter. Density is low, 2.4–2.6 g/cm3. Boron fiber is extremely strong and stiff with strength near 3.1 GPa (450 kpsi) and modulus near 400 GPa (58 Mpsi). The very high cost of these fibers (ca $1/g) has limited their use. (Harper CA (ed) (2002) Handbook of plastics, elastomers and composites, 4th edn. McGraw-Hill, New York).