At the end of 1918, upon his return from World War I, he settled his practice in Berlin. The Einsteinturm and the hat factory in Luckenwalde established his reputation. The Hat Factory was commissioned in 1921, Mendelsohn's design included four production halls, a boiler, a turbine house, two gatehouses and a dyeing hall. The dyeing hall became a distinctive feature of the factory, the building was shaped with a modern ventilation hood that expelled the toxic fumes used in the dyeing process. The structure even ironically resembled a hat.