The role of the resin in a composite is to keep the fibre straight and prevent them from buckling.


There are two pertinent resins for Orthotic manufacture.

Thermoset Molecule Structure

Epoxy Thermosetting

  • Molecules with strong cross linked bonds between chains.
  • Chains and bonds are degraded with heat and do not reform


Epoxy thermosetting resins are the most commonly used in Orthotic applications. Epoxy resins have excellent mechanical properties.

A disadvantage in Orthotic science is the inability of thermosetting resins to be heat mouldable after curing. Orthoses made in this material cannot be heat adjusted. They need to be re-worked. 

Thermoplastic Molecule Structure


  • Molecules with weak bonds
  • Bonds can be broken down with heat
  • Bonds reform on cooling


The advantage of Thermoplastic composites is the ability to heat and adjust the material without degrading the quality.

Thermoplastic composites can be complex to process. It is often difficult to orientate and keep the fibres long. This sometimes forces a compromise in design. The properties of thermoplastics are much weaker in comparison to thermosetting resins