This essay of the temporary Working Group “100% Digital” of the Association “Process, Apparatus and Plant Engineering” PAAT in ProcessNet addresses characteristics of a digital twin from the user's point of view and is intended to help solution providers to give product development a customer-oriented direction. For this purpose, the different data models are described which play a role in the life cycles of chemical processes, plants, and products. In particular, for existing (brownfield) plants, essential aspects of the digital twin are subsequently formulated. Further expressions and consequences, e.g., on qualification and training, are deduced from the above.