The QUANTAPANEL 605-DH Architectural Low-e Storm Window installs on the interior of an existing double hung window. Installation of the QUANTAPANEL 600 Series is through pre-drilled holes via screws that attach to the window jamb perpendicular to the plane of the window. A compressible seal on the perimeter of the frame ensures a tight seal, and allows for slight out-of-square conditions in the window opening. This 2-track system has a removable upper sash, and an inner sash that opens vertically to adjustable heights to allow for fresh air ventilation. A distinguishing feature of the QUANTAPANEL 605-DH IGS is the minimal depth of less than 0.900 in. The patented QUANTAPANEL 605 Series provides for extremely low air infiltration, which is necessary for optimum performance of an interior secondary sash system. This product is ENERGY STAR certified. The QUANTAPANEL 605-DH Architectural Low-e Storm Window are available in standard or custom colors (185 colors to choose from)!