In this paper we will review and extend the results of [21], which covered the case of 3D thermo-piezoelectric polycrystals. In that context the settings of conductivity, elasticity, pyroelectricity, piezoelectricity, thermo-electricity and thermo-elasticity can be viewed as particular cases. We will consider a class of composites more general than polycrystals, where the set of allowable mater...