a flexible and reusable plastic window covering is designed to be selectively attached over an existing window opening to reduce or eliminate air leakage and drafts . either hook and loop fasteners or locking strips can be used to attach the plastic sheath over a window opening and , if desired , the sheath can be provided with a zipper to allow air flow through the window . special locking strips can be used to securely attach the flexible sheath over a window opening while facilitating an easy removal when required .