Designed to be the most energy efficient option Great Lakes Window offers, ecoSmart windows and patio doors offer center of glass U-factors as low as 0.111 (R 9.1) in all product styles, and total unit U-factors as low as 0.14 (R 7.1) in fixed units or 0.16 (R 6.3) in double hung units, the manufacturer reports. These values, achievable with a triple pane, krypton gas-filled glass package option, are said to provide more than double the insulating power of Energy Star-qualified low-E glass options and be more than nine times more energy efficient than single pane glass. Other energy efficiency features include high-density solid-polyurethane insulation in the frame and sash and the G-force reinforcement, a composite made from recycled materials, around the vinyl mainframes. For added aesthetics and security, double hung windows in the series come standard with the flush mounted locking system, featuring two integral lock/tilt latches that mimic traditional wood window hardware. Several interior/exterior color combinations are available, including a new dark bronze exterior option that closely matches the darker brown color common on older aluminum windows.