Glass Fiber vs Carbon Fiber Reinforced Thermoplastics: Complete Performance Comparison

The choice between glass fiber and carbon fiber reinforcement in thermoplastics is one of the most consequential material decisions in engineering design—affecting mechanical performance, processing behavior, part cost, and even electrical...

The choice between glass fiber and carbon fiber reinforcement in thermoplastics is one of the most consequential material decisions in engineering design—affecting mechanical performance, processing behavior, part cost, and even electrical properties. At the same fiber loading (e.g., 30%), carbon fiber produces a composite with approximately 2× the tensile modulus, 1.5× the tensile strength, significantly lower thermal expansion, and electrical conductivity—but at 3-5× the raw material cost per pound.

Head-to-Head Property Comparison (PA66 base resin, 30% fiber loading)

Tensile Strength: GF30: 180 MPa / CF30: 240 MPa (+33%). Flexural Modulus: GF30: 8.0 GPa / CF30: 18.0 GPa (+125% — the most dramatic difference). Notched Izod Impact: GF30: 10 kJ/m² / CF30: 7 kJ/m² (-30% — carbon fiber reduces toughness). Density: GF30: 1.37 g/cm³ / CF30: 1.28 g/cm³ (carbon fiber is lighter). CLTE (flow direction): GF30: 30 μm/m·°C / CF30: 12 μm/m·°C (carbon fiber provides dramatically better dimensional stability). Surface Resistivity: GF30: >10¹² Ω (insulator) / CF30: 10²-10⁵ Ω (conductive — enables electrostatic dissipation). Warpage: GF30: Moderate / CF30: Lower (carbon fiber's higher stiffness reduces differential shrinkage). Cost Multiplier vs Unfilled: GF30: 1.5-2× / CF30: 5-10×.

When to Choose Which

Choose Glass Fiber When: Electrical insulation is required (connectors, housings, circuit breaker components); Radio-frequency transparency is needed (antenna housings, radar covers); Budget constraints dominate; Impact toughness is critical over stiffness; The part is large and material cost dominates part cost; Processing requires lower screw and barrel wear. Choose Carbon Fiber When: Maximum stiffness-to-weight ratio is the primary design driver (aerospace brackets, drone components, racing parts); Dimensional stability under thermal cycling is critical (precision optical mounts, metrology fixtures); Electrostatic dissipation (ESD) is required (electronics handling trays, ATEX environments); Lower density justifies the cost premium through fuel savings (automotive, aerospace); Warpage control in complex geometries cannot be achieved with glass fiber alone.

Comparison at a Glance

Equivalents & Cross-References

Related Diagnostics & Materials

References & Industry Standards

• ASTM International. Standard Specifications for Engineering Plastics & Thermoplastics. astm.org
• UL Prospector. Plastics & Elastomers Material Database. ulprospector.com
• MatWeb. Material Property Data for Engineering Thermoplastics. matweb.com
• ISO 1043. Plastics — Symbols and Abbreviated Terms. iso.org