Wood fibres are (usually) cellulosic elements that are extracted from trees, straw, bamboo, cotton seed , hemp and sugar cane to name just a few sources. The dimensions of individual fibres typically used in North America can range from 0.5 mm to 30 mm (0.02" - 1.2") in length and 0.02 mm to 0.04 mm (0.0008" - 0.0015") in diameter. Specialty fibre length can be 130 mm (5") or longer, and as narrow as 0.009 mm (0.0003") in diameter.

The end paper product (paper, paperboard, tissue etc.) dictates the species, or species blend, that is best suited to provide the desirable sheet characteristics, and also dictates the required fibre processing (chemical treatment, heat treatment, mechanical 'brushing' or refining etc.).

In North America, virgin (non-recycled) wood fibre is primarily extracted from hardwood (deciduous) trees and softwood (coniferous) trees, of which there is an abundant and (if properly managed) virtually inexhaustible supply.

These treated wood fibres (which are often combined with other additives) are then processed into a network of wood fibres, which constitutes the sheet of paper.

Research about fibres is sometimes conducted by fibre simulation