Wood pulp fibers are mainly produced via sulfate and sulfite pulping processes. We use hardwood and softwood fibers from the sulfate process that is also known as the kraft process. The softwood fibers are on average 3 mm long while the hardwood fibers are shorter, up to 1 mm in length.

Wood pulp fibers are suspended in water to make an slurry. Additives such as retention aids and strength promoters may be added and the slurry is formed into sheets of paper (handsheets) that are used in the laboratory for analysis of the paper properties.