Formal structure and classification of theories of oriented materials

In the first part of the paper we discuss an equation of balance of generalized moment of momentum proposed earlier; we show that internal forces necessarily play a rôle in it; we put in evidence the formal structure of some theories of polar continua. In the second part we show that most cases of oriented materials studied so far can be interpreted as subcases of a general type, when appropriate kinematical constraints are introduced; this unifying point of view allows a clear classification of subcases. It becomes also possible to obtain, in a standard way, balance equations which are pure, in the sense that they do not involve internal reactions.