The QUANTAPANEL 502-PW 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. The sash is held in place by retaining bars, and is removable to the exterior. For larger windows, the QUANTAPANEL 502-PW can have two sashes with a meeting rail, and arched configurations can be fabricated as well. This product is ENERGY STAR certified for either the northern or southern region. The QUANTAPANEL 502-PW Architectural Low-e Storm Window is available in standard or custom colors (185 colors to choose from)!