We state a problem of mosaic rational reinforcement for plane thermo-elastic structures such that different criteria of rationality are used for different regions of the structure. The criteria used are as follows: uniform stress reinforcement, reinforcement along the directions of principal stresses or principal strains, rational reinforcement based on the criterion of strength for particular materials of the composition. We perform qualitative analysis of corresponding systems of governing equations. Studying some particular examples, we show that mosaic reinforcement give us an opportunity to design new structures with rational reinforcement or to improve effectiveness of structures as compared to the cases of usage of one criterion of rationality to whole the structure.