Buildings consume more than 40% of all the energy we use, and about 50% of it is used for the conditioning systems, for this reason it is important to work on the energy demand, improving the buildings behaviour, in order to save the environment of the future. And sustainability is the keyword. Light constructions, based on the structure/envelope model, where all the envelope's depth is filled with insulation, are the first step to a sustainable architecture. Active House Alliance is a non-profit organization supported and managed by a group of Alliance Partner working on the same vision: the natural step forward for the sustainability, the innovation in the answer of the buildings to the climate stress. The concept of the active house is based on a responsive (active) behaviour of the building, that it is no more an inertial shell but it is capable to answer instantly to the thermal strains, assuring the indoor comfort and saving energy. What makes that possible is the coupling of an innovative envelope, seen as a changeable membrane (due to the external conditions), with a management's automation system. An active house can change its configuration to meet the users need: for example opening the windows or shadowing it, activating the artificial ventilation or enhancing the natural one. The aim of the alliance is to understand the principles of the active buildings and spread the knowledge to a larger public; Politecnico di Milano, as member, investigates the energetic issues for the warm regions of Europe, while the other partners are more focalized on the cold climate regions. The idea of active has a double vision: active is the building behaviour, thanks to its physical features and to the management system, but active is also the skin of the house, thanks to the innovative materials used. The aim of the research is to understand the characteristics that make a building capable to answer itself to the thermal strains, but also how innovative nanomaterials, such as phase change materials and aerogel, could affect the performances. This innovation, especially the coupling of phase pcm to the envelope, thanks to their cyclical capability of taking heat from the room and give it back later, summarize and materialize the possibility of having an active envelope that could assure indoor comfort minimizing the energy request.