The fixed chamber balers are soft core. The Variable chamber balers give a hard core. It's in baler design. A fixed chamber is kinda like rolling into an empty drum, the more hay you put in the more dense the bale gets. The center 18" or so can only get so compressed, hence the soft core. The variable chamber, like the one in the picture, starts with a smaller diameter center and hydraulicly resists the rolling bale. Packing it tighter.