Scattering Model for Composite Stereolithography to Enable Resin–Filler Selection and Cure Depth Control

Fillers are used to modify the properties of the photoresins used in stereolithography (SLA). The resulting composite formulations tend to have a decreasing cure depth for increasing particle loadings due to light scattering. However, some composites, such as those loaded with silica or polymethyl methacrylate particles, show the opposite effect: the cure depth increases with the particle loading. To unify these seemingly contradictory observations, we propose a modified Lambert–Beer equation. Depending on the filler properties, we differentiate between three scenarios: (i) scattering-dominated, (ii) weakly scattering, and (iii) nonscattering (refractive index-matched). In the first case, the cure depth of the resin decreased with an increasing solid loading, whereas in the other cases, the opposite trend was observed. These findings have significant implications for the formulation of composite SLA resins in terms of materials selection and printing parameter optimization.