The standard size filter element shall be constructed of a single piece of heavy-duty, one piece craftboard frame. The metal grid shall be thermally bonded internally to the frame. The metal grid shall be 28 gauge and provide 82% open area. All corners shall be closed and sealed. The filter media shall be constructed in a progressively dense fashion from air-entering to air-leaving side. The PolyStrand® filter media shall be made from fibers completely coated with a polyester coating. Glasfloss disposable panel filters shall be rated to withstand temperatures up to
180 degrees Fahrenheit. All filters shall be Classified under U.L. std. 900.