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Carbon Fiber Grades Explained: T300, T700, T800 and IM7

20 April 2026
4 min read

Why Carbon Fiber Grade Selection Matters

Carbon fiber is not a single material — it is a family of materials with substantially different mechanical properties, processing characteristics, and price points. Specifying T300 when your application requires T800 results in an underperforming part. Specifying IM7 for a structural tube that T700 can handle adds unnecessary cost. Understanding what each grade offers is a prerequisite for sound composite engineering.

The grading nomenclature largely follows Toray's classification system, which has become the de facto global standard.

Key Mechanical Properties to Understand

  • Tensile strength: Load per unit cross-section at which the fiber breaks. Measured in MPa or GPa.
  • Tensile modulus (Young's modulus): Stiffness — ratio of stress to strain within the elastic region. Higher modulus means less deformation under load.
  • Elongation at break: How much the fiber stretches before failure, as a percentage. Higher elongation generally correlates with better damage tolerance.

T300: The Industry Baseline

T300 is the original commercial carbon fiber grade, introduced by Toray in the 1970s.

  • Tensile strength: ~3,530 MPa
  • Tensile modulus: ~230 GPa
  • Elongation at break: ~1.5%

T300 remains widely used for non-structural applications, tooling, and cost-sensitive structural parts where modest performance is sufficient. It is the most readily available and lowest-cost standard modulus fiber, making it a default choice for general industrial composites, sporting goods, and interior aerospace components.

T700: Improved Strength, Similar Stiffness

T700 improves on T300's tensile strength without increasing modulus — targeting applications needing more load-carrying capacity but not greater stiffness.

  • Tensile strength: ~4,900 MPa
  • Tensile modulus: ~230 GPa
  • Elongation at break: ~2.1%

The higher elongation improves damage tolerance and reduces risk of catastrophic failure under impact loading. T700 has largely displaced T300 in structural automotive, wind energy, and pressure vessel applications. It is the standard fiber for filament-wound CNG and hydrogen storage cylinders.

T800: Higher Strength and Slightly Higher Modulus

  • Tensile strength: ~5,490 MPa
  • Tensile modulus: ~294 GPa
  • Elongation at break: ~1.9%

T800 grades are used extensively in aerospace primary structures — Boeing 787 and Airbus A350 wing structures — where the combination of high strength and elevated stiffness enables significant weight savings versus aluminium. The price premium over T700 is substantial, making T800 correct only where its specific properties are structurally justified.

IM7: Intermediate Modulus, Exceptional Strength

IM7, produced by Hexcel, is the North American aerospace industry's standard intermediate-modulus fiber.

  • Tensile strength: ~5,516 MPa
  • Tensile modulus: ~276 GPa
  • Elongation at break: ~1.9%

IM7 is specified extensively in defence and space applications: structural aircraft components, satellite structures, and launch vehicle sections. Its aerospace qualification history and supply chain integration make it the fiber of choice when regulatory traceability and heritage qualification are requirements.

Practical Grade Selection Guidelines

  • General industrial and non-structural: T300 or T700
  • Automotive structural, pressure vessels, wind blades: T700 for cost-optimised performance
  • Commercial aerospace primary structure: T800 or IM7 per design authority specification
  • Defence, space, high-performance motorsport: IM7 or higher-grade intermediates per qualification programme

At GLB Composites, we supply T300, T700, T800, and IM7 in a range of tow sizes and fabric architectures. Our technical team can assist with material selection for specific structural requirements and processing constraints.