AbstractResin composites have been in the dental field for over forty years. They are nowthought to be the most commonly used restorative material due to their aesthetic andmechanical properties. Although resin composites have high success rates asrestorations, they do not offer all properties of an ideal restorative material. The aimsof this research were to characterise the effects of variation in resin compositeformulation on handling, mechanical; and physical properties. In particular theinfluence of the size and distribution of the inorganic components was investigatedthrough the study of experimental formulations.Packing stress and viscosity were assessed with pentrometer principle at twodifferent temperatures (23 and 37 ºC). It was found that filler size was stronglycorrelated with both packing stress and viscosity. Additionally, temperature has adominant effect on packing stress and viscosity.Micro computed tomography [μCT] was used to investigate percentage of voids[% voids] in 3D dimensions. It was found that smaller filler size incorporated less %voids. In contrast filler size and disruption had a little effect on fracture toughness ofresin composites.3D surface topography was used to investigate the surface roughness before and aftertooth brush abrasion. It was found filler size had a significant influence in both glossretention and surface roughness (smaller filler size exhibited higher surface gloss).Finally, the effect of different storage media (distilled water, Coca Cola and redwine) on colour stability and gloss were investigated. It was found that dietary habitseffect discolouration of resin composite restorations with the acidic drinks causedmore staining.