Following the First World War mill architecture began to evolve and reflected the broader trends shaping industrial architecture of the time, particularly that which Albert Kahn had been developing for the automobile industry. The great innovations came in the forms of reinforced concrete and steel.
Reinforced concrete, concrete which is combined with steel rods to create a material of exceptional strength and flexibility, quickly replaced wood and brick as the primary building material for industrial structures such as paper mills. The material had the advantages of being exceptionally strong, easily capable of supporting heavy machinery, fire proof, and could be built quickly. For single-story structures, the use of exposed steel beams became increasingly common.
With the use of concrete and steel, walls were no longer supporting the weight of the structure and could be opened up to allow more light. The segmental arched wooden windows of earlier mill buildings gave way to large steel sash window frames that could fill the entire space between structural columns. On upper levels additional light could be allowed in via monitor or sawtooth roofs. Mill interiors became very light and airy, although difficult to heat in the cold months.
Examples of this type of industrial architecture were Plant #2 of the Kalamazoo Vegetable Parchment Company and the Power House of the Bryant Paper Mill.