Recycled paper is made from waste paper, usually mixed with fresh wood pulp. If the paper contains ink, it must be deinked. This also removes fillers, clays, and fiber fragments.
Almost all paper can be recycled today, but some types are harder to recycle than others. Papers coated with plastic or aluminum foil, and papers that are waxed, pasted, or gummed are usually not recycled because the process is too expensive. Gift wrap paper also cannot be recycled. Different types of paper are usually sorted before recycling, such as newspapers and cardboard boxes.
Different grades of paper are recycled into different types of new products. Old newspapers are usually made into new newsprint, egg cartons, or paperboard. Old corrugated boxes are made into new corrugated boxes or paperboard. High-grade white office paper can be made into almost any new paper product: stationery, newsprint, magazines, or books.
Sometimes recyclers ask for the removal of the glossy inserts from newspapers because they are a different type of paper. Glossy inserts have a heavy clay coating that some paper mills cannot accept. Most of the clay is removed from the recycled pulp as sludge which must be disposed. If the coated paper is 20% by weight clay, then each ton of glossy paper produces more than 200 kg of sludge and less than 800 kg of fiber. Uncoated (no clay), recycled newsprint gives less sludge and more useable fiber.
Paper can only be recycled a finite number of times due to the shortening of paper fibers making the material less versatile. Often it will be mixed with a quantity of virgin material, referred to as downcycling. This does not however exclude the material from being used in other processes such as composting or anaerobic digestion, where further value can be extracted from the material in the form of compost or biogas.