Two-flux models are practical tools for predicting the appearance of strongly scattering materials, but may fail to predict the spectral reflectance factor of translucent (i.e. weakly scattering) materials because of the simplifying as-sumptions upon which they are based. In a previous study, we showed how the internal reflectance at the interface of translucent layers, a parameter usually cal-culated assuming a Lambertian angular light distribution, can be adjusted in order to consider a directional light distribution, thus improving the predictive perfor-mance of the two-flux model applied to translucent dental resin composites. In this paper, we explore the dependence of this parameter on the layer’s thickness and show how different values should be considered for accurately predicting the spectral reflectance factor of either thin or thick layers of translucent direct resin composites according to their thickness. We also extend the model to the layering procedure of resin with different levels of opacity which usually belong to the category of thick layers and show that the two-flux model can reach good predic-tion accuracy for their spectral reflectance factor.