The key is whether a chemical pre-treatment step was used before mechanical defibration. Purely mechanical pulp (4701) involves no significant chemical softening, while semichemical pulp (4705) requires a defined chemical cooking stage followed by mechanical separation. Mill process documentation or a technical specification sheet is typically needed to confirm the production method.

While corrugating medium is by far the dominant end use — because the retained hemicellulose provides the stiffness needed for fluting — semichemical pulp is also used in some specialty board grades and as a blend component in certain printing papers where stiffness is valued. Its relatively high yield compared to kraft pulp also makes it cost-competitive for high-volume packaging applications.