Abstract: An elongated flange material for forming a flange and a method for use in sealing a non-flanged window, door, or other fenestration product in a wall opening, wherein the flange material comprises at least one top coversheet and at least one bottom coversheet with a pressure-sensitive adhesive layer sandwiched between the two coversheets, wherein the coversheets occupy an appreciable width of the flange but do not extend across the entire width of the flange and thereby are offset with respect to each other thereby providing opposing first and second exposed surfaces of the pressures sensitive adhesive layer.