A mattress cover and bed bug barrier combination formed of a fabric mattress cover having walls that define an enclosure with an elongated opening extending in at least one of the walls, a zipper attached to the cover for closing the elongated opening, the cover having seal regions laterally adjacent the distal portion of the zipper, a seal element secured to each of the seal regions, an external barrier flap having a first part fixed to the cover, and a second part foldable from an open position where it is spaced apart from the seal elements to a closed position where it is folded down to overlie and seal against the seal elements, and thereby provide a barrier to travel of bed bugs inwardly or outwardly of the cover through the distal portion of the zipper when the zipper in its closed state.