A flexible cover having magnetic attachment is provided for sealing openings in a structure such as a heating, ventilation and air conditioning duct, an automobile window, or an automobile door handle or lock. Magnets or another suitable affixing device are attached at the periphery on one side of the cover. Alternatively, the magnets may be attached to one side of the cover by sandwiching the magnets between two opposing flexible covers. Gaps between the magnets permit the flexible cover to attach to objects having a curved or angular conformation. In operation, the cover is placed over the opening preventing the transmission of air, fluid material, or particulate material through the opening.