In context of industry 4.0, a digital twin provides new opportunities
for production optimization and failure prediction. Therefore, both
industry and scientific research show increasing interest in digital
twins. One of the most important sectors in the production value chain
is material science, which plays a very important role for the product
properties and processing strategies. However, the digital microscopic
and macroscopic description of materials' properties and its processing
are currently not fully defined. Therefore, in order to implement
materials into the digital representations of production processes, a
throughout digital description of the material and its properties -- a
digital material twin -- is presented in this paper. An extended digital
material twin is further defined and includes the processing history.
Thus, a throughout description of the material is enabled. The extended
material twins can be connected to a process chain. Thus, we describe
the concept for a comprehensive description of the materials' properties
within the production value chain. For more complex, data intensive,
descriptions, a concept to reduce the data, the digital material shadow
is introduced as well. Our approach defines a framework to thoroughly
describe a material and its development during processing or production.