By the method of initial functions (MIF) in a rectangular Cartesian coordinate system Oxy. The behavior of products made of foamed materials is investigated on the basis of the moment theory of elasticity. The initial functions in the MIF solution are represented by trigonometric series, which made it possible to solve the boundary problem of deforming a micropolar rectangle (h × l) with arbitrary boundary conditions on the sides x = 0, h and free support (σy = 0, u = 0, µy = 0) on the sides y = 0, l. The results of computational experiments showing the effect of the ratio of rectangle sizes and its height for the manifestation of the “size effect” for syntactic foam and polyurethane foam are presented. The minimal linear dimensions of the rectangle are determined, with a decrease in which it begins to manifest itself “size effect”.