From Fig. 9a, it can be seen that the flexural strength of pure epoxy was 49.9 MPa, but increased to a maximum value of 64 MPa for the composite containing 4 vol% nano-sized WO3. However, a further increase in the filler loading beyond 4 vol% resulted in a decrease in flexural strength whereby the composite containing 10 vol% nano-sized WO3 exhibited the lowest flexural strength of 52.6 MPa. Similarly for micro-sized WO3-epoxy composites, the maximum flexural strength was obtained for a filler loading of 2 vol%. A reduction in flexural strength was again observed when the filler loading was increased beyond 2 vol% due to non-uniform dispersion of the filler within the matrix. The resultant agglomeration of the fillers acted as stress-concentrators which served to reduce the strength of the composites.