Paper is a thin, flat material produced by the compression of fibers. The fibers used are usually natural and composed of cellulose. The most common source of these kinds of fibers is wood pulp from pulpwood trees, (largely softwoods) such as spruce. However, other vegetable fiber materials including cotton, hemp, linen, and rice may be used. Though generally considered a flexible material, the edges of paper sheets can act as very thin, fine-toothed saws, leading to paper cuts.

Manufacturing

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Whether done by hand or with a paper machine, the paper making process has three simple steps:

Preparation of the fibers

The material to be used for making paper is first converted into pulp, a concentrated mixture of fibers suspended in liquid. The source of fiber is often natural (softwood or hardwood trees or other plants) or recycled, such as old corrugated boxes, newsprint, or mixed paper.

When best sheets materials are used to make paper, it is usually necessary to break down the lignin inside of the plant's cell walls. This is done via a chemical process, such as the Kraft process. These processes are not needed when breaking down recycled fibers, as the lignin has already been removed from the source material. If the lignin is retained in the pulp, the paper will yellow when exposed to air and light.

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