A cover window of a flexible display device includes a base substrate including an out-folding area, an in-folding area, and peripheral areas disposed on opposing sides of at least one of the out-folding area and the in-folding area, a first hard coating layer at a top surface of the base substrate, the first hard coating layer having a substantially uniform thickness, and a second hard coating layer at a bottom surface of the base substrate opposite to the top surface, the second hard coating layer having a thickness different from the thickness of the first hard coating layer. A thickness of a first area of the second hard coating layer that overlaps with the out-folding area and the in-folding area of the base substrate is less than a thickness of a second area of the second hard coating layer that overlaps with the peripheral areas of the base substrate.