The QUANTAPANEL 506-SL Architectural Low-e Storm Window installs on the exterior of an existing window, and can be installed in either a blind stop or overlap fashion. This 2-track system has a removable sash and removable screen in the outer track, and an inner sash that opens horizontally to allow for fresh air ventilation. All sashes remove to the interior for cleaning and maintenance. The QUANTAPANEL 506-SL can be ordered in a 2-sash or 3-sash configuration. The low-profile design integrates with the existing window providing an unobstructed view of the existing primary window. This product is ENERGY STAR certified for the northern or southern region. The QUANTAPANEL 506-SL Architectural Low-e Storm Window is available in standard or custom colors (185 colors to choose from)!