Proposed is a flexible cover window including a window substrate and an elastic buffer layer having a single-layer structure or a multi-layer structure. The elastic buffer layer is provided on the rear surface of the window substrate to absorb deformation occurring in a folding part. The flexible cover window is a glass-based cover window for protecting a flexible display that is foldable, rollable, slidable, or stretchable. In addition, the flexible cover window has an elastic buffer layer on the rear surface of the window substrate to reduce the difference in elongation between the window substrate and a display panel so that delamination or buckling due to micro-deformation at the folding part thereof can be prevented. Therefore, the life span of the flexible cover window is prolonged and distortion of an image on the screen at the folding part can be prevented.