Paper pulp is a wet, fibrous material made by breaking down wood or other plant matter into individual cellulose fibers. Those fibers are then reformed into sheets to make paper, cardboard, packaging, and dozens of other products. At its core, pulp is mostly cellulose, the same structural molecule that gives plants their rigidity, mixed with smaller amounts of other plant compounds depending on how it was processed.
What Pulp Is Made Of
Wood is not a single substance. It’s a composite of cellulose (the strong, flexible fibers), hemicellulose (a shorter-chain molecule that acts as a binding agent between fibers), and lignin (a rigid compound that makes wood stiff and brown). The goal of pulping is to free the cellulose fibers from the lignin that holds them together.
The chemical makeup of finished pulp varies depending on how aggressively the lignin was removed. Bleached pulp, the kind used for white office paper, is roughly 78 to 79% cellulose, about 20% hemicellulose, and less than 2% lignin. Unbleached softwood pulp still contains around 9% lignin, which is why products like brown kraft paper bags have that characteristic tan color. At the far end of the spectrum, thermomechanical pulp retains about 31% lignin because the wood is pulled apart physically rather than chemically dissolved.
How Wood Becomes Pulp
There are two broad approaches to turning wood into pulp: mechanical and chemical. Each produces a different type of fiber with different strengths, and most paper products use one or a blend of both.
Mechanical Pulping
Mechanical pulping grinds or shreds wood chips into fibers using physical force, sometimes with steam to soften them first. The big advantage is yield: up to 90% or more of the original wood ends up as usable pulp, meaning very little raw material goes to waste. The tradeoff is that the fibers are shorter, weaker, and still full of lignin. Paper made from mechanical pulp yellows over time as the leftover lignin reacts with light. Newsprint and magazine paper are classic mechanical pulp products.
Chemical Pulping
Chemical pulping uses a hot chemical bath to dissolve the lignin and separate the fibers more gently, which preserves their length and strength. The dominant method worldwide is the kraft process (kraft means “strength” in German). Wood chips are cooked in a solution of sodium hydroxide and sodium sulfide, known in the industry as white liquor. This solution breaks apart the chemical bonds in lignin through a series of reactions at high temperature, eventually removing up to 90% of the lignin from the wood.
The kraft process yields less usable fiber per log than mechanical pulping, but the fibers it produces are longer, more flexible, and significantly stronger. That’s why kraft pulp is the backbone of corrugated boxes, grocery bags, and any paper product that needs to hold weight or resist tearing. The leftover liquid, called black liquor, contains the dissolved lignin and spent chemicals. Mills burn this liquid to recover energy and recycle the cooking chemicals back into the process, making kraft mills largely self-sufficient in energy.
Softwood vs. Hardwood Fibers
Not all trees produce the same kind of pulp. Softwoods like pine and spruce have long fibers, typically 1.6 to 2.0 mm, which interlock well and create strong paper. Hardwoods like eucalyptus and birch have much shorter fibers, around 0.7 to 0.8 mm, which produce a smoother, more uniform surface. Most paper products blend the two: softwood fibers for structural strength and hardwood fibers for a better printing surface and softer feel. Tissue paper, for instance, relies heavily on short hardwood fibers for softness.
Specialized Types of Pulp
Beyond standard paper-grade pulp, there are specialty grades designed for entirely different industries. Dissolving pulp has an extremely high cellulose content, above 90%, with almost all the hemicellulose and lignin stripped away. It’s not used for paper at all. Instead, it’s the raw material for rayon fabric, cellophane, and cellulose-based chemicals found in products from food thickeners to pharmaceutical coatings.
Fluff pulp is another specialty grade, processed into thick, absorbent sheets that are then shredded into a fluffy fiber mat. It’s the absorbent core inside diapers, feminine hygiene products, and adult incontinence pads. The fibers are chosen and processed specifically for their ability to wick and hold liquid.
How Pulp Gets Bleached
Raw chemical pulp is brown because of residual lignin. To make white paper, mills put the pulp through a multi-stage bleaching sequence that breaks down and removes remaining lignin without damaging the cellulose fibers. Historically, mills used elemental chlorine gas, which was effective but produced toxic chlorinated compounds in wastewater.
Today, the standard across most of the global industry is Elemental Chlorine Free (ECF) bleaching, which substitutes chlorine dioxide for chlorine gas. This dramatically reduces the formation of harmful byproducts. A smaller number of mills use Totally Chlorine Free (TCF) processes, relying on oxygen and hydrogen peroxide instead. TCF pulp is marketed as a more environmentally friendly option, though ECF remains far more common.
Recycled Pulp and Its Limits
Used paper can be turned back into pulp by soaking it in water and mechanically breaking it apart again. This recycled pulp gets mixed with fresh virgin fiber to make new paper products. But recycling has a physical ceiling. Each time fibers go through the process, they get shorter, stiffer, and weaker. The EPA estimates paper fibers can be recycled five to seven times before they’re too degraded to bond into a usable sheet. Some industry estimates put the practical limit at four to six cycles. After that, the fibers are too short and must be replaced with fresh pulp.
This is why recycled paper products almost always contain some percentage of virgin fiber. It’s also why lower-grade products like cardboard and egg cartons tend to use more recycled content than fine printing paper, which demands longer, stronger fibers.
Global Production
World wood pulp production reached 189 million tonnes in 2024, up 3% from the prior year. Brazil has become a major force in the industry, along with Chile and Uruguay, where fast-growing eucalyptus plantations give South American producers a cost advantage. China has also expanded its pulp production significantly. The United States, Canada, and the Nordic countries remain major producers, particularly of the kraft pulp used in packaging.
The shift toward e-commerce has reshaped demand. While printing and writing paper volumes have declined in many markets, demand for containerboard (the material corrugated boxes are made from) continues to grow, keeping pulp mills busy even as fewer people print documents.