In the flat window, the sliding window and the fixed window form a single flat surface when the window is closed, so there is no layer difference in the window. This allows the user to enjoy an optimal panoramic view. When viewed from indoors, the window looks like a single glass pane, making the space look more spacious. Although a sliding window, the design minimizes the gap between the window and window frame. The application of triple glazing results in insulation performance of 1 W / m² K.