The extremals of the minimal layer thickness problem for reflectance modification, given monochromatic waves at normal incidence and real material parameters, are analyzed. The structures of sublayer sequences leading to minimal total layer thickness, when both the density and the dilatation modulus are allowed to vary independently are presented. It is found that there exist two different sublayer sequences. Both are periodic with unit cells of four layers. Minimal sequences for the corresponding one‐parameter problems are obtained as limiting cases.