Thermoplastics can provide composites with a greater fracture toughness than is possible with thermosetting resins.
A disadvantage of thermoplastics for use as matrix materials for continuous fibre reinforcements is that, due to the high viscosity of polymer melts, it is very difficult to achieve sufficient infiltration of the fibre bundles by the polymer. Fibre preforms consisting of the reinforcing fibres co-mingled with fibres of the matrix polymer are commonly used to make thermoplastic matrix composites. The preform is then hot pressed to shape. This causes the matrix polymer to melt and flow into the spaces between the reinforcing fibres.