Abstract: An interior window cover assembly is provided for selective insulating sealable closure of a window opening so as to prevent air infiltration and reduce heat transfer therethrough. The window cover assembly is provided with a pair of vertically oriented spaced-apart track assemblies adapted for opposed sealable engagement with the vertical sides of a window frame. A horizontally oriented spring-actuated window cover roller assembly is pivotally mounted across the top of a window frame in abutting engagement with the upper ends of the track assemblies. A flexible insulating window cover member having a sill closure bar across the bottom thereof is selectively extendable downwardly from the window cover roller assembly so as to cover the window opening. The vertical edge portions of the flexible cover member extend into grooves provided in the track assemblies and are movable therealong as the sill closure bar is moved downwardly to draw the window cover member over the window opening.