After the Second World War, steel and concrete continued to be important building materials for industrial structures and paper mills. However, due to improvements in artificial lighting and air conditioning systems, the importance of a large number of windows and skylights diminished drastically. In fact, due to the high heat-loss associated with large numbers of windows, post-war structures had far fewer windows, if any at all. And often windows on older buildings would be covered up. Exterior walls became blank canvases of corrugated steel and aluminum.
Both the Kalamazoo Paper Company and the Mac Sim Bar complexes included post-war structures.