Corrugated Cardboard...
Corrugated cardboard is one of the most recycled materials in America: over 80 percent of it is diverted from the landfill. Cardboard goes through a shredding, cleaning, slurry process similar to other paper. Then, it almost always gets formed into new cardboard boxes.
another cool aspect to these facilities is the way they ingeniously sort materials from each other. they use air gusts, lasers, mechanical means and even electron streams to separate stuff out. the electron streams for example are used to sort magnetic from non magnetic metal.