Plastic user interfaces have the capacity of adapting themselves to their context of use while preserving usability. This property gives rise to several versions of the same UI. This paper addresses the problem of verifying UI adaptation by means of formal methods. It proposes three approaches, all of them supported by the CADP toolbox and LNT formal language. The first approach permits the reasoning over the adaptation output, i.e. the UI versions: some properties are verified over the UI models thanks to model checking. The second solution proposes to verify the plasticity engine. The last approach compares UI versions thanks to equivalence checking. These approaches are discussed and compared on an example of a system in the nuclear power plant domain.