Pulp grades are classified according to their production process.
They are classified by original species: softwood or hardwood and by the production process used: chemical or mechanical and bleached or unbleached
Stone Groundwood pulp: by grinding wood into relatively short fibres. This pulp is used mainly in newsprint and wood-containing papers, like LWC (lightweight coated) and SC (super-calendered) papers
Thermo-mechanical pulp (TMP): produced in a thermo-mechanical process where wood particles are softened by steam before entering a pressurised refiner. TMP has mainly the same end-uses as stone groundwood pulp. Variants of the above two processes are pressurised stone groundwood pulp and refiner mechanical pulp.
Semi-chemical pulp: produced in a similar way to TMP (thermo-mechanical pulp), but the wood particles are chemically treated before entering the refiner. This pulp has properties suited to tissue manufacture. Some chemi-thermo mechanical pulp (CTMP) pulp is used in printing and writing grades. CTMP pulp is classified under semi-chemical pulps in the Harmonised System of the Customs Cooperation Council. In the Food and Agricultural Organisation (FAO) of the United Nations, as well as other industry statistics, such chemi-thermo mechanical pulps are grouped with mechanical pulp.
Sulphite pulp: produced by cooking wood chips in a pressure vessel in the presence of bisulphite liquor. End-uses range from newsprint, printing and writing papers, tissue and sanitary papers. The sulphite can be either bleached or unbleached.
Sulphate (or kraft) pulp: pulp produced by cooking wood chips in pressure vessels in the presence of a sodium hydroxide (soda) liquor. The pulp may be unbleached or bleached. End-uses are widespread, with bleached pulp particularly used for graphic papers, tissue and carton board, wrappings, sack and bag papers, envelopes and other unbleached speciality papers.
Pulp made from recovered paper from which inks and other contaminants have been removed.