Cooper Historical Windows recognized early on that glass is the most important element in accurately reproducing or restoring any historical window. We believe that “glass is the engine that drives the window”. Since restoration glass is rarely flat, it was not possible to effectively use it in an insulated glass unit, limiting its energy efficiency and economic appeal. Recognizing the industry’s need to fill this void, we decided to set our focus on developing a restoration glass that is always flat, enabling us to build single pane glass and insulated glass units to the very highest standards, matching most cylinder glass from 1800 to 1920. Today, our Liberty Restoration Glass IGUs look historically accurate and deliver the best energy performance values in the industry.