You can use material flow diagrams to illustrate material flows between functions. In modeling, they are treated similarly to information flow diagrams. In a material flow diagram, you link two functions by means of a material flow connection. This connection indicates a material flow from the source function to the target function. If you want to further specify the material that is input for or output of the functions displayed, you can assign a material diagram to this connection, which results in the formation of a hierarchy for this material flow connection. The material diagram serves to illustrate the material or material types exchanged between the functions.