The wood used to produce pulp mostly comes from tree thinnings and waste products from saw mills, the bulk of whose timber production goes into construction and furniture making. The industry once relied on woods such as spruce, pine, larch, fir and cedar, but now woods such as birch, aspen and other hardwoods are also used, particularly for fluting. Australasian Eucalyptus has also been successfully cultivated in warm climates, including South America, Spain and Portugal.
Different species yield different grades of wood fibre, with location also playing a role.
Northern Europe trees are popular as a result of their long fibres, providing strength for high quality papers. Trees grown closer to the Equator, on the other hand, tend to have shorter fibres. In the Kraft process, caustic soda and sodium sulphate are used. The sulphite process, which tends to result in easily bleached pulps, is becoming increasingly popular in disposable sectors. The by-produced waste resulting from the chemical processes can be reprocessed as a fuel substitute and several paper mills have thus become power suppliers to local electricity grids.