The Bending-Gradient plate theory originally presented in  is applied to cellular sandwich panels. This theory is the extension of Reissner-Mindlin theory to heterogeneous plates. Its application clarifies common assumptions made in sandwich theory. It also enables to define a direct homogenization scheme for deriving the shear forces stiffness of sandwich panels. Finally, the conventional bounds used for estimating sandwich panels stiffnesses are justified. To cite this article: Arthur Lebée, Karam Sab, C. R. Mecanique ?? (201?).