High quality papers are made from long fibers. The four most common fibers used in the Orient to make paper are Mulberry, Kozo, Gampi, and Mitsumata. Many of the fine art papers commonly found in the US are made from cotton or wood pulp, also called sulphite. Cotton is naturally acid free and is manufactured in two grades or qualities of paper making fibers. The highest grade is cotton rag made from fine fabric grade fibers, which are long and strong.
Wood pulp is another popular fiber in paper manufacture.
Wood pulp is plentiful and fairly inexpensive, however is acidic by nature and must be buffered to produce a pH neutral paper. Because wood pulp is comprised of short fiber, lower and mid-quality papers are produced. However, recent technologies have been able to produce alphacellulose removing the acid causing component, lignin. Papers made from alphacellulose rival in quality those papers made from cotton rag. The thickness of a paper is decided by the paper maker and is measured in a number of ways.