AbstractThis paper shows the results of a research activity aimed at assessing the advantages of an ideal adaptive building skin over conventional building envelope systems.The basic idea underlying the research consists in imagining an ideal building envelope system characterised by the capability of continuously changing (within a certain range) some of its thermo-physical and optical properties. The reason for the continuous tuning of thermo-physical and optical properties lies in the assumption that an optimised (fixed) configuration, where the properties do not change over time, is not able to minimise the total energy demand of the building at each moment.For the sake of this purpose, an ideal dynamic WWR (Window-to-Wall Ratio) building envelope system for low energy office buildings was modelled and simulated. An integrated, commercial thermal-lighting building simulation tool (EnergyPlus) was used to perform the calculation. The energy performance of such a system was then analysed and compared against the performance of a conventional façade realised with best-available technologies.The results of the investigation demonstrated the advantages of a dynamic WWR configuration over a static one. However, the improvements achieved in energy demand were lower than expected. This behaviour is strictly related to the configuration of the building used as a reference, which already showed a very high energy performance.Limitations presented by the research method are also briefly pointed out and discussed.