A duct filter bag used in connection with a heating and air conditioning vent, the duct filter bag including a filter body constructed of a material that is air permeable yet catches particles exiting the vent, the filter body having a perimeter; an attachment assembly connected to the filter body; where the filter body is extendable outward relative to the attachment assembly to define a filter volume; the attachment assembly being adapted to attach the filter body such that the filter volume is in registry with the vent.