We conduct experimental and theoretical study of the effect of polymer coatings on the mechanical properties of the samples in the form of steel plates. It is shown that, despite the fact that the thickness of the coating is 100 microns, it has a significant effect on the mechanical properties of the plate with thickness of 1.5 mm, resulting in a decrease of Young’s modulus and tensile strength of the samples. It is shown that tensile and bending tests cannot uniquely identify the elastic modulus of the coated plate. In the bending test it is more significant reduction in stiffness of the plates, compared to the tensile test. This effect is confirmed
by calculations in the framework of classical models of the theory of elasticity.