Paper originated in China in about AD 105. It reached Central Asia by 751 and Baghdad by 793, and by the 14th century there were paper mills in a number of places in Europe. The invention of the printing press in about 1450 markedly increased the need for paper, and at the beginning of the 19th century wood and other vegetable pulps began to replace rags as the main source of fibre for papermaking.

Before 1798, Nicholas-Louis Robert invented the earliest paper-making machine. With a moving screen belt, paper was made one sheet at a time by the dipping of or mould which has a screen bottom into a vat of pulp. Some years later the brothers Henry and Sealy Fourdrinier improved Robert’s machine, and then in 1809 John Dickinson invented the first cylinder machine.

Although nearly all of the steps in papermaking have become highly mechanized, the basic process has remained mostly the same. First of all, the fibres are separated and wetted to produce the paper pulp, or stock. The pulp is then filtered on a woven screen to form a sheet of fibre, which is pressed and compacted to squeeze out most of the water. The remaining water is removed by evaporation, and the dry sheet is further compressed and, depending upon the intended use, coated or impregnated with other substances.

Differences among the grades and types of paper are decided by several factors: the type of fibre being used; the preparation of the pulp, which is either by mechanical (groundwood) or chemical (primarily sulfite, soda, or sulfate) methods, or by a combination of the two; by the addition of other substances to the pulp, the most commonly used being bleach or colouring and sizing, the latter to impede penetration by ink; by conditions under which the sheet is formed, including its weight; and by the physical or chemical treatments applied to the resulting sheet.

Although wood has become the major source of fibre for papermaking, rag fibres are still used for paper of maximum strength, durability, and permanence. Recycled wastepaper (including newsprint) and cardboard are also important sources. Additional fibres used include straw, bagasse (residue from crushed sugarcane), esparto, bamboo, flax, hemp, jute, and kenaf. Some paper, particularly specialty items, is made using synthetic fibres.

Weight or substance per unit area, called basis weight, is measured in reams (now commonly 500 sheets). Paper is also measured by caliper (thickness) and density. The strength and durability of paper is determined by factors such as the strength and length of the fibres, as well as their bonding ability, and the formation and structure of the sheet. The visible properties of paper include its brightness, colour, opacity, and gloss. Among the most important paper grades are bond, book, bristol, groundwood and newsprint, kraft, paperboard, and sanitary.

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