The double skin of the enclosure acts as an air duct and thermal buffer, ‘breathing’ by opening and closing different panels. In combination with the mass of the concrete structure, which is a passive thermal store that is further heated and cooled by piped water inside the structure, it acts in response to Berlin’s varying climate. In lower temperatures (below 6°c), the external skin closes like a cocoon and fresh air is drawn through an undercroft and warmed as it passes through by the thermal core. In moderate temperatures (above 16°), a mix of fresh and recirculated air is cooled by the core. While for 60 percent of the year, the library can be entirely naturally ventilated by opening various panels and using controlled fresh air drawn in through the undercroft. During the day the library is entirely naturally lit. These factors mean that the library will consume 35 percent less energy than a comparable building.