Chemi-thermo mechanical pulping (CTMP) involves the application of chemicals to the wood chips before refining. The process starts with the penetration of 2% to 5% of sodium sulfite and chelating agents at a pH of 9 to 10. The mixture is heated for 2 to 5 minutes at the temperature of about 120 to 130 °C and is subsequently refined. The yield of unbleached softwood CTMP is in the range of 86% to 90%. Pre- steaming is done to remove air from the woodchips and stabilise the chip temperature. The chemical pre-treatment of the chips permits less destructive separation of fibers from the wood resulting in a higher longer fiber content and a much lower shive content than thermomechanical pulp. CTMP proved a higher brightness before bleaching and is better suited for absorbent grades and food packaging.

Improvements in this process, such as increasing the first stage refiner speed and decreasing the pH of the sulfite liquor, allows additional energy savings (Martin et al., 2000. p.25-26).