A gas filtering device of the type having a pleated filter media for filtering a gas stream passing through the media from the upstream side to the downstream side of the filter device, a peripheral frame surrounding and attached to the margin of the pleated filter media, a filter media reinforcing device comprised of an elongated rigid beam disposed within a pleat of the pleated filter media and extending the entire length of the pleat, and filter media retaining means attached to the rigid beam and extending across the downstream side of the filter media.