The interest in polymer composites research is due to their enlarged application. Filling with hard particles gives to polymers a number of desirable properties: increases hardness, decreases heat expansion coefficient, improves resistance to creep and fracture toughness. Difficulties in structure-properties relationships researching for polymer composites are due to their structure complexity. Till now, composites studies were conducted within the frameworks of continuum mechanics and thermodynamic conceptions. However, these conceptions applications does not allow satisfactory descriptions nor predictions of such materials properties. As a matter of fact, an experimental data set dictates one or another physical model of structure choice for composites macroscopic properties description.