Technically, in ABA type film, the outer and inner layers will be of the same material fed by the same extruder and a middle layer will be of a different material that will be fed by a second extruder. A higher percentage (up to 50-70%) of calcium carbonate compounds or recycled material can be used in the middle layer of the film, thus cutting down the usage of virgin raw material and reducing production cost. http://www.cnebpmmachine.com/blown-film-machine/aba-blown-film-machine/