Filter bags consist of a box with a funnel at its base. The filter sleeves made of felt or woven material, and open at their upper end, are suspended side by side. The sleeves can be threaded on bases in the shape of flat or cylindrical frames which prevent their deformation under the pressure of the gases. The gases loaded with dust collide first with a deflector to separate the largest dust particles. The gases then pass through the sleeves from the outside to the inside. The dust is retained on the outer surface of the sleeves and cakes into one layer (filter cake). This filtration system is recommended for the retention of fine dust and gaseous pollutants.