Flexible window and flexible display device including the same

A flexible display device comprising:

• a display panel which displays an image with light;
• and
• a flexible window disposed on the display panel, to which the light is incident from the display panel and from which the light exits the flexible display device,
• the flexible window comprising:
• a first film layer through which the light is incident to the flexible window from the display panel, the first film layer comprising:
• a plurality of stacked first sub-film layers,
• an adhesive layer disposed between adjacent first sub-film layers, and
• an index matching layer disposed between a first sub-film layer and
• the adhesive layer adjacent thereto;
• and
• a second film layer which is on the first film layer to be disposed further from the display panel than the first film layer, the second film layer having a Young's modulus lower than that of each of the first sub-film layers,
• wherein within the flexible window, a refractive index of the index matching layer has a value between a refractive index of each of the first sub-film layers and a refractive index of the adhesive layer.