Alumina Fiber vs Glass Fiber: Properties Compared
Glass fiber dominates composites by volume thanks to low cost and good all-round performance. Alumina continuous fiber costs far more — but it works where glass fiber physically cannot: sustained temperatures above roughly 500°C.
Head-to-Head Comparison
| Property | Alumina Continuous Fiber | Glass Fiber (E-glass type) |
|---|---|---|
| Max continuous service temperature | 1000–1600°C | ~260–500°C depending on product form |
| Tensile strength | 1700–2000 MPa | High — valued for strength in composites |
| Tensile modulus | 140–185 GPa | Roughly one-half or less of alumina fiber |
| Density | 2.7–3.4 g/cm³ | ~2.5 g/cm³ (lighter) |
| Oxidation / heat degradation | None — stable ceramic oxide | Softens and loses strength above ~500°C |
| Electrical insulation | Good | Very good — a classic insulator |
| Chemical resistance | Very good | Good; attacked by strong alkalis |
| Relative cost | High (specialty ceramic) | Low (commodity fiber) |
| Availability | Few global producers | Ubiquitous worldwide |
| Textile processability | Woven or braided with the aid of protective sizings; brittle ceramic filaments need careful handling | Very easy — flexible filaments weave, knit, chop, and spray readily |
| Typical product forms | Tow, roving, yarn, woven fabrics, tapes, and sleevings | Rovings, yarns, woven and non-woven fabrics, mats, chopped strands, and prepregs |
| Handling durability | Brittle — filaments fracture if bent sharply or abraded | Tough and flexible at room temperature; standard textile handling |
Glass fiber temperature limits vary with product form: glass wool insulation is typically limited to about 260°C, while glass fiber mats and textiles serve up to roughly 400–500°C. Above that range, alumina fiber is the practical step up.
When Glass Fiber Is Enough
- Service temperatures stay below ~400°C — the vast majority of polymer composites, building insulation, and electrical applications.
- Cost is the primary driver: glass fiber is orders of magnitude cheaper per kilogram.
- High production volumes and established supply chains matter.
- Electrical insulation at moderate temperatures is the main requirement.
When to Upgrade to Alumina Fiber
- Temperatures exceed 500°C continuously: exhaust systems, furnace zones, kiln furniture, and hot-gas paths.
- Stiffness matters at temperature: alumina's 140–185 GPa modulus is roughly double or more that of glass fiber, and it retains stiffness where glass softens.
- Oxide-oxide composites: for aerospace and energy components that must survive oxidizing atmospheres at 1000°C+.
- Molten metal contact: aluminum foundry and filtration applications where glass would degrade.
Pros and Cons
Alumina Fiber
- Sustained service at 1000–1600°C — works where glass physically cannot.
- High stiffness (140–185 GPa) that is retained at temperature, roughly double or more that of glass.
- None of glass's softening or strength loss above ~500°C; stable in oxidizing atmospheres.
- Suitable for contact with molten metals and slags.
Alumina Fiber
- Far higher cost — a specialty ceramic versus a commodity fiber.
- Brittle filaments that need careful textile handling.
- Limited supply: few global producers and longer lead times.
- Denser (~2.7–3.4 g/cm³) than glass (~2.5 g/cm³).
Glass Fiber
- Extremely low cost and ubiquitous global availability.
- Very good electrical insulation at moderate temperatures.
- Easy textile processing and a huge range of product forms.
- Proven, high-volume performance in polymer composites and insulation.
Glass Fiber
- Softens and loses strength above ~500°C — unusable in hot zones.
- Modulus roughly one-half or less of alumina's 140–185 GPa.
- Attacked by strong alkalis.
Selection Checklist
- Does the continuous service temperature exceed ~500°C?
- Must the material keep its stiffness at operating temperature?
- Is electrical insulation the main function, rather than heat?
- Does the production volume demand commodity pricing and global supply?
- Will the part contact molten metal or slags?
- Is oxidation resistance required at temperature?
Common Mistakes
- Assuming all glass fiber handles 500°C: glass wool insulation is typically limited to about 260°C — only glass fiber mats and textiles reach roughly 400–500°C. Check the product form, not just the material name.
- Running glass continuously above ~500°C: it softens and loses strength; that duty belongs to alumina fiber.
- Ignoring the stiffness gap: glass fiber's modulus is roughly half or less of alumina's 140–185 GPa, so deflection-critical designs don't translate directly.
Bottom line: glass fiber wins on cost, availability, and moderate-temperature performance. Alumina continuous fiber wins decisively wherever sustained heat above ~500°C, high stiffness, or oxidation resistance is required. Compare also alumina vs aramid fiber and alumina vs carbon and basalt fibers.