The fabric filter unit consists of one or more insulated compartments containing rows of fabric bags in the shape of round, flat or shaped tubes, or pleated cartridges. The particles contained in the exhausted air move along the surface of the bags, then radially through the fabric. The particles are retained on the upstream face of the bags and the clean gas stream is discharged to the atmosphere. The filter is operated cyclically, alternating with relatively long filtering periods and short cleaning periods. During cleaning, the dust that has accumulated in the bags is removed. Fabric filters collect particles ranging in size from submicron to several hundred microns in diameter with efficiencies generally greater than 99 or 99.9 percent. The layer of dust, or cake of dust, collected on the fabric is primarily responsible for such high efficiency. The cake is a barrier with tortuous pores that trap particles.