Abstract: A self-supporting filter unit having at least one passage (10) defined by wall portions (12) made from air-permeable fiber fabric, through which wall portions air can pass and be drawn off along the passage but which prevent the passage therethrough of dust and/or other debris carried by such air, in which the passage is closed off at one end portion and at the other end portion there is formed integral with said wall portions a rigid mounting portion (16) into which the passage (10) opens whereby the filter unit can be supported as part of a filter assembly, wherein the mounting portion (16) includes a first reinforcing portion (18) of material around and secured with said fabric of the wall portion parts of the first reinforcing portion and fabric integral therewith remote from said one end being outwardly flanged, and wherein the mounting portion (16) further includes a second reinforcing portion (20,21) of material positioned over the outwardly flanged portions and secured thereto, said second reinforcing