The damage behavior of polymeric composites can be improved considerably by thermomechanical treatment. In this paper the relevant mechanisms causing this improvement are discussed in detail. It includes the physical and mechanical properties of the pure matrix before and after the thermomechanical treatment, as well as micromechanical mechanisms. The experimental results show that a thermomechanical treatment causes a high amount of permanent deformation of the matrix but no essential changes in its mechanical properties.The micromechanical calculations indicate an almost constant absolute value of permanent deformation of matrix across the entire fiber radius and consequently no changes of local stresses. Therefore, the treatment causes only a change in fiber distance, which results in a permanent deformation of transverse plies of the multidirectional laminate. Additional requirements for the mechanical properties of fibers and matrix in order to achieve a successful treatment are suggested from this approach.