The containment wall of a basket media mill is constructed of a porous synthetic polymeric material having porous openings each of a pore size less than the predetermined size of the media for confining the media within the bed in the basket as feedstock is passed through the porous openings in the containment wall. The containment wall extends over an overall area and the porous openings provide an open area through which the feedstock flows as the feedstock passes through the containment wall, and the open area is at least about fifteen percent of the overall area of the containment wall for enabling a concomitant increased volumetric flow of feedstock through the containment wall. A substantially flat sheet of porous synthetic polymeric material having porous openings is formed into a cylindrical configuration to establish a cylindrical containment wall with porous openings each increasing in pore size from the interior of the cylindrical wall toward the exterior of the cylindrical wall.