Glass Fiber (Inorganic / Silica-Based Reinforcement Fiber)
Glass fiber is the most widely produced inorganic reinforcement fiber — approximately 7 million tons per year, predominantly E-glass. It is made by melting silica sand (SiO₂) with alumina, calcium oxide, and boron oxide at ~1400°C, then extruding the molten glass through platinum-rhodium bushings with thousands of fine holes. The filaments are rapidly cooled, sized with a chemical coating for protection and matrix compatibility, and wound onto rovings. The result is a high-strength, electrically insulating, incombustible fiber that costs $2–5/kg — the workhorse of composite reinforcement, thermal insulation, and printed circuit board substrate. Its brittleness (2.5–4.8% elongation, no plastic deformation) is the critical design constraint.
Quick Facts
| Type | Inorganic; melt-spun from silica-based glass (SiO₂ + Al₂O₃ + CaO + B₂O₃ + MgO etc.) |
| First commercialized | 1930s (Owens Corning); continuous filament 1938 |
| Global production | ~7 million tons/year (largest-volume inorganic fiber); E-glass dominates (~90%) |
| Density | 2.5–2.6 g/cm³ (heavier than organic fibers; lighter than metals) |
| Tensile strength | 2.0–3.5 GPa (E-glass); 4.5–5.0 GPa (S-glass / high-strength) |
| Elongation at break | 2.5–4.8% (brittle; no plastic deformation) |
| Softening point | ~850°C (E-glass); continuous service to ~600°C |
| Key types | E-glass (electrical, general), S-glass (high strength), C-glass (chemical resistant), AR-glass (alkali resistant for cement) |
Properties
| Property | Rating | Engineering implication |
|---|---|---|
| Strength | ★★★★☆ | High tensile strength at low cost; the workhorse composite reinforcement |
| Stiffness | ★★★☆☆ | Modulus 70–85 GPa; adequate for most FRP; below carbon and aramid |
| Heat resistance | ★★★★☆ | Softens ~850°C; incombustible; no melting — decomposes gradually |
| Electrical insulation | ★★★★★ | Excellent dielectric; the 'E' in E-glass stands for Electrical |
| Chemical resistance | ★★★☆☆ | C-glass for acid; AR-glass for alkali (cement); E-glass attacked by strong alkali |
| Brittleness | ★★☆☆☆ | Low elongation; sudden failure; surface defects cause dramatic strength reduction |
| Cost | ★★★★★ Low | $2–5/kg; the most cost-effective reinforcement fiber |
Summary
Glass fiber is the volume leader in inorganic reinforcement — cost-effective, strong, electrically insulating, and incombustible. Its brittleness and moderate stiffness confine it to applications where cost per unit strength matters more than ultimate performance. See the Textile Material framework.