[en] A relationship for the buildup factor of two-layer shielding for point isotropic and plane-paralles sources has been obtained. Buildup factor formula is based on the substitution of the second layer of the shielding by the equivalent layer from the first material and the subsequent approximate definition of the equivalent thickness of the second layer. The corresponding nomogram and curves calculated with the formula for different thicknesses of heavy material are given. The desing and experimental results are compared. The error of the buildup factor experimental determination is no more than 15%