Creating something sustainable out of glass is a challenging proposition. Glass production is an energy-intensive process, as it requires furnaces running constantly with temperatures upwards 1600°C. Tystø is a partitioning system made from reclaimed glass units, which in their first life cycle have been used as façade or roof windows. The windows are carefully taken out of the building as a part of a demolition or renovation process and subsequently disassembled into frame and glass units. The glass units are obsolete for exterior windows and are thus, normally, destined for elimination. However, they may live a long second life as indoor partitions, where they replace the conventional, heavily polluting glass. All materials, apart from the doors, are collected, processed, and produced in Denmark. Doors are manufactured in Riga.