Three-point bending tests were used to determine the flexural strength and modulus of the WO3-epoxy composites containing different loadings of nano-sized and micro-sized WO3. Specimens with dimensions 60 mm × 10 mm × 2 mm were prepared for the test according to the ASTM D790-03 standard [20] on a universal testing machine (LLOYD Instruments). A minimum of three samples was tested for each composite and the average results were taken. In these measurements, the samples were tested to the applied load with the results calculated by the NEXYGEN Plus software.