Silk fibers combine good stiffness and strength with a very high strain to failure and are as such highly promising to realize composites with high impact resistance. It is shown that to realize this potential it is quite beneficial to employ matrix materials of high strain to failure, particularly thermoplastic matrices. High impact resistance is thus achieved, well above the values for the pure matrices. Below the glass-transition temperature of the thermoplastic matrix, the impact energy absorption decreases. The adhesion between fiber and matrix also plays a significant role; lower adhesion typically increases the low-velocity penetration impact resistance, due to the spread of damage. Finally, the fiber architecture is pivotal; when a woven fabric is used which is unbalanced in strength, the impact resistance reduces in correspondence with the weakest material direction. A quasi-isotropic layup has a lower capacity for deformation than a balanced woven configuration which likely explains the observed lower penetration impact resistance.

The combination of ductile Bombyx Mori silk fibre with ductile thermoplastic matrices, combined with the use of a woven fibre architecture, leads to ductile composites with quasi-isotropic strength. Bending and tensile properties were determined for (0,90)_s silk twill weave composites, with different thermoplastic polymers and as reference epoxy resin. Thermoplastic (0,90)_s woven silk fibre composites are isotropic in strength (about 135 MPa at 50% fibre volume fraction) due to the high elongation to failure of both the silk fibre and the thermoplastic matrix allowing extensive shearing of the silk fabric when loaded in the 45° direction. A good quality interface has a clear positive influence on the mechanical properties especially on the bending yield strength.