Abstract: An improved encasement for a mattress which thwarts the escapement of bed bugs from a mattress through the encasement and which thwarts the encroachment of beg bugs through the encasement into the mattress. An elongated opening is provided in the encasement which is selectively closed by a zipper associated therewith. The encasement includes a flap secured to the lower side wall portion of a side of the encasement which is positioned inwardly of the zipper for retarding or preventing the escapement of bed bugs through the zipper. Hook and loop fasteners are also provided at the end location for further preventing the escapement of bed bugs from the mattress through the encasement and preventing the encroachment of beg bugs into the mattress through the encasement.