Filler-reinforced polymers have gained increasing attention from X-ray technologists in radiation shielding since polymers have great potential in many important applications by virtue of their unique properties, such as low density, the ability to form intricate shapes, optical transparency, low manufacturing cost and toughness. One of the filler-reinforced polymers commonly used for radiation shielding is lead acrylic [14], [15] and [16]. Moreover, some researchers have also tried to synthesise nano-sized filler-reinforced polymers for radiation shielding by virtue of the size effect in X-ray attenuation [2], [6] and [17]. For instance, a recent study by Botelho et al. [13] revealed that the attenuation for X-ray beams generated from low tube voltages (i.e., 26–30 kV) in nanostructured copper oxide (CuO) was better than microstructured CuO. However, no significant difference in attenuation was observed for X-rays generated from higher tube voltages (i.e., 60–102 kV). A similar conclusion on this size effect in X-ray attenuation was made by Kunzel et al. [18] for a nanostructured CuO-polymer system.