There are five basic grades of paper: old corrugated containers, mixed paper, old newspapers, high grade deinked paper and pulp substitutes. Old corrugated containers are more commonly known as “corrugated cardboard” and are usually found in boxes and product packaging. Paper mills use recycled corrugated cardboard to produce shipping boxes, as well as recycled paperboard for cereal boxes, shoe boxes and other product packaging. Mixed paper is a broad category that includes mail, telephone books, magazines and catalogs. Mills use mixed paper to produce paperboard and tissue, as a secondary fiber in new paper and as a material in non-paper products like chipboard and egg cartons. Old newspapers are, of course, discarded newspapers and are primarily recycled back into newsprint. They are also used in paperboard and tissue. High grade deinked paper includes letterhead, copier paper and envelopes that have already gone through the printing process. This grade of paper has to be deinked before it can be made into high grade paper products like printing paper or tissue. Pulp substitutes are another high grade paper and are often made up of shavings and clippings from converting operations at mills or print shops. Mills use pulp substitutes in the place of raw materials to make high grade paper products. Shredded paper is not its own grade, but it can be recycled as long as it is shredded to an appropriate size and is mostly free of contaminants, such as plastics.