Most engineers know carbon fiber is electrically conductive. Fewer realize it is also thermally anisotropic - and this property can make or break your design.
Along the Fiber (Axial)
High-modulus carbon fibers, especially pitch-based types, conduct heat exceptionally well along their length - thermal conductivity can reach 500-900 W/mK, rivaling copper. This makes carbon fiber an excellent heat spreader in one direction.
Applications:
Heat sinks in LED arrays (fiber direction aligned to heat source)
Thermal management in satellite structures
Dissipating heat from power electronics in drone frames
Across the Plies (Transverse)
Perpendicular to the fiber direction, the epoxy matrix dominates. Thermal conductivity drops to 0.5-1.5 W/mK - effectively an insulator. This is why a carbon fiber plate feels cold on one edge but warm on the surface.
Applications:
Thermal barriers between hot components and sensitive electronics
Cryogenic tank supports (minimizes heat leak into cold contents)
Fire-resistant panels where one side faces high temperature
Design Implications
|
Scenario |
Recommendation |
|---|---|
|
Need heat dissipation |
Align fibers toward heat source; use pitch-based fiber |
|
Need thermal insulation |
Load perpendicular to fibers; increase ply count |
|
Mixed requirement |
Hybrid laminate: conductive outer ply + insulating core |
|
High-temp environment (>150°C) |
Switch to BMI or phenolic resin matrix |
Common Mistake
Specifying carbon fiber as a "heat shield" without defining fiber orientation. A plate with all 0° plies will conduct heat straight through - the opposite of what you want. Always state whether heat flows parallel or perpendicular to your part's primary axis.
