Aim Resin composite (RC) are commonly used under full crowns. However, independent information is lacking to guide practitioners regarding core RC material selection. This study aimed at comparing the flexural properties of a large selection of commercially-available core build-up RCs (CBU-RC), either light-, self- or dual-cure, to conventional light-cure RCs. Methods RCs were injected into a 25 × 2×2mm Teflon mold, and either light-cured during 20 s (materials with claimed light-cure characteristics) or covered by aluminum during 10 min (dual- and self-cure CBU-RCs). They were subjected after a one-week water storage at 37.5 °C to three-point bending, and Flexural modulus ( E flex ) and Flexural Strength ( σ f ) were calculated ( n = 20). Thermogravimetric analysis ( n = 3) was performed to determine inorganic filler content (%). Results For dual-cure CBU-RCs, both RC ( p < .0001) and light-curing ( p = .0007) had a significant influence on E flex , while only RC was significant for σ f ( p < .0001). Between all conventional RCs and CBU-RCs, significant differences were observed ( p < .0001), both regarding E flex and σ f , with values ranging from 3.9 to 15.5 GPa and from 76 to 130.3 MPa, respectively. Higher E flex values were observed for light-cure RCs than for self- and dual-cure ones, while no clear trend was noticed regarding σ f . Good linear correlation was found between inorganic filler content and E flex ( R 2 =0.85, p < .0001), but not with σ f ( R 2 =0.08, p = .1609). Conclusion This work demonstrated a positive influence of light-curing on dual-cure CBU-RC’s E flex . It also highlighted large differences in flexural properties (especially E flex ) among the investigated materials, questioning the use of some CBU-RCs as dentin replacement in case of large tissue loss.