The aim of this study was to evaluate whether a post-cure heat-treatment may improve the flexural strength of two indirect resin-based composites. Tested factors were: material (Gradia Indirect, Gradia Forte), mass (opaqus dentin, dentin, enamel) and curing mode (light, light and heat). A three-point bending test appliance was developed according to ISO 4049/2000. Three-Way ANOVA and 2-Pameter Weibull cumulative distribution function were performed. Factors material and curing mode were significant (p < 0.001), while the mass type was not (p = 0.181). A post-cure heat treatment may be useful for enhancing the flexural strength of both materials