Johns Manville FSK-25 is a flame-retardant vapor barrier facing manufactured using 0.0003 lightweight aluminum foil, fiberglass reinforcing yarn and natural kraft paper laminated together with a flame-retardant adhesive. FSK-25 facing is designed for use over unfaced fiberglass insulation in applications that require faced insulation to comply with ASTM E-84 and is attached to the wall or ceiling with staples or mechanical fasteners.