Abstract: Apparatus for increasing the densichamber driven by a compression ram having a preset stroke and preferably being hydraulic, and a movable backplate facing the piston and being provided with means for producing a reaction force in opposition to the compression force of the ram and less than the maximum compression force exertable by the ram. Means for binding the compressed bales is also provided. Preferably the reaction force is maintained constant regardless of displacement of the backplate and this can be achieved by using a second hydraulic ram to which fluid is supplied at a constant pressure.