Wood fibers are usually cellulosic elements that are extracted from trees and used to make materials including paper.
The end paper product (paper, paperboard, tissue, cardboard, 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 fiber is primarily extracted from hardwood (deciduous) trees and softwood (coniferous) trees. Wood fibers can also be recycled from used paper materials.
Wood fibers are treated by combining them with other additives. They are then processed into a network of wood fibers, which constitutes the sheet of paper.