The paper presents a belt material model of a radial tire as a two-dimensional, orthotropic rubber-cord system. The rubber must absorb the energy developed in the composite material. The rigidity of the complex body is provided primarily by the cord-foundation which also must absorb energy developed in the strengthening plies. The rubber is considered an incompressible body due to its mechanical response. The simplest cord-strands show a bilinear behavior; their modulus of elasticity is dependent on their loading.The mechanical behavior of the belt forms part of the overall elastic characteristics of the composite body. The physical equation of the orthotropic rubber-cord system describes the relationship between the stresses acting on the material model and the values of the deformation as a function of the rubber and cord values. By means of the elasticity equation the material values of the composite body can be defined and determined. Comparison and testing of different cord structures of differing materials can be performed with the material values.