an inflatable storm window is disclosed which is adapted to be positioned within a window frame to both provide insulation and prevent air leakage around the regular window sash . the inflatable storm window comprises a continuous hollow outer portion of tubular cross section formed from a pliable and expandable plastic . a transparent sheet of film is peripherally attached to the inner edge of the continuous hollow outer portion . installation in the window frame is accomplished by inflating the hollow outer portion through a valve contained in the tubular sidewall .