Abstract: A method and apparatus for densification of fibrous material such as harvested cotton, preferably by a movement of the cotton continuously through a compacting zone on the harvester. In one aspect of the invention, the fibers are locked by differential translation of portions of the mass of compacted material to prevent a layer of material from springing back after compression. A continuous mat of compressed material with locked fibers is formed into a uniform, high density bale or module on the harvester. A cotton harvester compacting system includes an air system feeding harvested cotton into an accumulation area and to the compacting zone on the harvester. The cotton is compressed and fed through a shear zone which differentially translates the cotton and locks the cotton fibers into a uniform, compact mat. In one embodiment, the mat of compacted cotton is fed to a round baler on the harvester to form a dense round bale or module.