Delivering state-of-the art window performance while retaining the original architecture of a building’s windows is a critical aspect of architectural preservation. Windows are a critical element of the architectural character of any building. For historic structures, the form, design, materials and craftsmanship often capture design elements of the period in which the building was constructed. A building’s windows are a not only a critical design feature, but encompass critical functionality: a source of natural light into the building, a view, articulation between interior and exterior, ventilation (in some cases), comfort, insulating performance and heating/cooling implications. The QUANAPANEL Architectural Low-e Storm Window System can be installed on either the interior or exterior of the existing windows. Either option operates in conjunction with the existing window to provide thermal properties that are nearly equivalent to new windows in terms of U-factor (insulating performance), SHGC (solar heat gain) and visible light transmission (VT). The choice of interior vs. exterior depends to a large extent on the type of building and the merits and feasibility of exterior vs. interior installation. The QUANTAPANEL 600 Series (interior) installs to be nearly indistinguishable from the original window from both the interior and exterior of the building, and can be specified to be either fixed or operable (for fresh air ventilation). The QUANTAPANEL 500 Series (exterior) installs on the exterior of the building, thereby creating an additional protective barrier to the original window. The low-profile design and selection of style and color options provide several different design approaches. The coated glass and architecturally-coated aluminum components are durable, and there are no seal systems subject to failure. The use of architecturally appropriate low-e storm windows is recognized and advocated by the U.S. National Park Service Technical Preservation Services.