Abstract: Apparatus and method for installing loose-fill or dense pack fiberglass or cellulose insulation that is blown dry into the wall cavity of a building structure includes a drapeable sheet of fabric having a first region impermeable to passage of air and a second region contiguous with the first region, the second region being permeable to passage of air. The drapeable sheet of fabric is attached to the wall studs defining a plurality of cavities in the walls of a building structure. Once enough of the loose or dense packed fibers of fiberglass or cellulose to provide the desired degree of insulation has been blown into each of the cavities, then the second region of the sheet is covered at each cavity with a non-permeable strip so as to render the second region non-permeable to passage of air.