paper

Paper is a thin, flat material made by forming plant fibers into sheets and drying them. The primary raw material is wood pulp from softwoods and hardwoods, but paper can also be produced from cotton, linen, hemp, straw, and other fibers. It serves as a medium for writing, printing, packaging, and a wide range of other applications.

Manufacturing involves converting fibers into pulp, refining and mixing with water, and forming the slurry into sheets on a moving screen or felt. The sheets are pressed to remove water and then dried. Finishing steps may include calendering for smoothness, coating to improve print quality, and sizing to control absorbency. Properties such as grammage (mass per unit area), caliper (thickness), brightness, opacity, and strength depend on fiber source, pulping method, and finishing.

There are many paper types, including writing and printing papers, newsprint, packaging papers (such as kraft and liner), tissue, and specialty papers. Grades differ by weight, whiteness, absorbency, and texture. Paper is often graded by its intended use, with standards set by industry bodies and, for some products, by regional regulations.

Historically, papermaking originated in China, traditionally dated to the 2nd century CE with the work of Cai Lun, and spread to the Islamic world and Europe by the Middle Ages, accelerating with the invention of the printing press.

Recycling is a common practice to recover fibers; processes include de-inking and re-pulping. Paper production and disposal involve energy, water, and chemical use, and sustainable practices are supported by certifications such as FSC and PEFC.