How Paper is Made · The Complete Guide

Paper is a sheet material made from cellulose fibres, the structural component of plant cell walls, suspended in water, deposited onto a surface, and dried into a bonded mat. The fibres bond to each other through hydrogen bonds between their cellulose hydroxyl groups when the water is removed. No adhesive is required, the fibres bond themselves during drying. This natural bonding is what gives paper its characteristic properties: flexibility, printability, and the ability to absorb and release moisture.

Almost all printing paper in India is made from wood cellulose, extracted from softwood trees (eucalyptus, pine, spruce) or hardwood trees (birch, aspen, tropical hardwoods). A small but growing proportion is made from agricultural residues (bagasse from sugarcane, wheat straw) or from recovered (recycled) paper fibres. Each fibre source produces different paper properties.

The raw material, specifically the wood species and whether the fibre comes from softwood or hardwood, determines the fibre length, which in turn determines the paper's strength, printability, and folding performance.

Softwood fibres · long and strong

Softwood trees (eucalyptus grown in India, pine, spruce in Scandinavia and North America) produce long cellulose fibres, typically 2–5mm in length. Long fibres create more fibre-to-fibre bonds per unit area, producing a strong, tear-resistant paper with good folding endurance. They are the primary fibre source for:

• Packaging board (particularly SBS and kraft paper) where strength is the priority
• Paper requiring high folding endurance, banknotes, maps, technical manuals
• The kraft layer in corrugated board linerboard

Hardwood fibres · short and smooth

Hardwood trees (birch, eucalyptus in some pulp grades, tropical hardwoods) produce shorter fibres, typically 0.7–1.5mm. Short fibres pack together more densely, producing a smoother surface and better formation (more uniform distribution of fibres across the sheet). They are the primary fibre source for:

• Coated art papers and premium printing papers where surface smoothness is the priority
• Copy paper, the smooth surface feeds reliably through laser and inkjet printers
• A blend of short hardwood and long softwood fibres is used for most commercial printing papers, the hardwood provides smoothness and the softwood provides strength and tear resistance

Non-wood fibres

• Bagasse (sugarcane residue), India produces significant quantities of bagasse paper, particularly for lower grades. Bagasse fibres are shorter than wood fibres and produce papers with adequate printing quality but lower strength than wood-based papers.
• Cotton / rag fibre, produces the highest-quality uncoated papers: banknote paper, archival papers, premium stationery. Cotton fibres are almost pure cellulose with no lignin, they do not yellow with age and last for centuries. Very expensive. Watermarks are formed in cotton papers during manufacture.
• Wheat straw and agricultural residues, increasingly used in India as an alternative to wood pulp for economy grades. Variable quality.

Pulping is the process of separating wood into individual cellulose fibres. There are two fundamentally different approaches, chemical pulping and mechanical pulping, and the choice between them determines the paper's whiteness, strength, and longevity. This is the distinction that separates SBS board (all chemical pulp) from FBB board (chemical top and back plies, mechanical middle) from newsprint (almost all mechanical pulp).

The paper machine converts a dilute aqueous suspension of fibres, approximately 99% water, 1% fibre, into a dry sheet at speeds of 400–1200 metres per minute. Each section of the machine serves a distinct purpose in removing water and forming the sheet structure.

The headbox and forming section (Fourdrinier wire)

The dilute fibre suspension is ejected from the headbox, a precisely engineered flow distributor, onto the forming wire: a moving mesh of fine plastic or bronze wire. Water drains rapidly through the wire, and the fibres deposit on its surface. As the fibre suspension flows rapidly in one direction, the fibres align preferentially with the direction of travel, this is the origin of paper grain direction. The machine direction becomes the grain direction.

• The wire section removes approximately 80% of the water by gravity and vacuum drainage
• The two-sidedness of paper originates here, the wire side (bottom) has a slightly different surface texture from the felt side (top), because the wire leaves a faint texture on the bottom surface. On uncoated papers, this difference is visible and measurable. On coated papers, the coating equalises both sides.
• Paper formation, the uniformity of fibre distribution, is set here. A well-formed paper has consistent density and opacity across its area. Poor formation (uneven clumping of fibres) produces mottled, uneven ink absorption on press.

The press section

The wet paper web, still containing approximately 80% water at the end of the wire section, passes through a series of press nips, pairs of rollers that squeeze the web under high pressure. The water is transferred to felt blankets (not the same as printing blankets, these are thick, porous absorptive felts). The press section reduces water content from approximately 80% to approximately 60%.

• Press pressure affects paper density, higher press pressure produces denser, smoother paper with lower bulk
• Extended nip pressing (shoe press), a modern development that applies press pressure over a longer area, produces more uniform moisture content and better paper formation than conventional roll presses

The drying section

The pressed web, now at approximately 60% moisture, passes over a series of steam-heated cast-iron cylinders, typically 50–100 cylinders arranged in a tunnel-like structure. The moisture evaporates as the web contacts the hot cylinders. By the end of the drying section, the paper is at 4–6% moisture content, the equilibrium moisture content for standard press room conditions.

• The rate of drying affects paper properties, fast drying at high temperature can produce internal stress and curl
• The drying cylinders also set the grain direction more firmly, the shrinkage that occurs as the web dries is different in the machine direction (where the web is held under tension) and the cross direction (where it can shrink freely). This differential shrinkage is part of what makes the cross-direction more moisture-responsive than the machine direction.

Size press (surface sizing)

After drying but before calendering and coating, many papers pass through a size press where a dilute solution of starch or synthetic size is applied to both surfaces of the web. Surface sizing improves:

• Ink holdout, the size partially seals the surface, reducing ink penetration
• Surface strength, reduces linting and picking during printing
• Dimensional stability, sized fibres are more resistant to moisture uptake
• Most quality printing papers and board grades receive surface sizing. Economy newsprint and tissue papers generally do not.

Calendering

The dried and sized web passes through a calender stack, a series of polished hard rollers that compress and smooth the paper surface under high nip pressure. Calendering:

• Reduces surface roughness, improves print quality and ink holdout
• Increases gloss (for gloss papers)
• Reduces caliper, heavier calendering produces thinner, denser, smoother paper at the same GSM
• Machine calendering (on-machine): standard for most papers, moderate smoothing. Supercalendering (off-machine): much more aggressive, produces high-gloss surfaces on mechanical papers like magazine stock.

Coating (on-machine or off-machine)

For coated papers and boards, a mineral coating slurry (kaolin clay and calcium carbonate with binder) is applied to one or both sides. This can be done in-line on the paper machine (on-machine coating) or in a separate coating operation (off-machine coating). The difference affects quality and economics, off-machine coating generally produces higher-quality surfaces because the base paper is fully dried and stable before coating is applied.

Reeling and sheeting

The finished paper is wound onto large parent reels at the end of the paper machine. These reels are then either:

• Slit and rewound into narrower rolls for web offset printing presses
• Cut into sheets at a sheeting machine, sheets are cut to standard sizes (A1, SRA1, etc.) and packaged into reams (250 or 500 sheets)

Every property of a printed sheet that matters to quality, colour density, dot sharpness, register stability, folding behaviour, post-lamination curl, traces directly back to a specific step in the papermaking process. Understanding these connections allows better diagnosis of press problems and better specification decisions.

Recycled paper is made from recovered paper fibres that have been de-inked, cleaned, and re-formed into new paper. It is an important part of the sustainability picture for the print industry, but its properties differ from virgin paper in ways that directly affect print quality.

What happens to fibres when paper is recycled

• Each recycling cycle shortens and weakens the cellulose fibres, they break during the pulping and cleaning process
• After approximately 5–7 recycling cycles, the fibres are too short and weak to form paper without virgin fibre addition
• Recycled fibres retain residual ink and filler particles even after de-inking, the whiteness of recycled paper is inherently lower than virgin bleached paper
• Recycled fibres from recovered newspapers and mixed waste contain residual lignin, the recycled paper may yellow faster than virgin chemical pulp paper

Print quality differences

• Lower whiteness and brightness, greyish or cream tonal cast compared to virgin bleached papers. Colours appear less vivid and shadows appear less deep on recycled paper.
• Lower surface strength, recycled fibres are shorter. Surface picking is more common on recycled papers, particularly with high-tack inks or at high press speeds.
• More variable caliper and formation, the mixed fibre content of recovered paper produces more batch-to-batch variation than virgin paper from a consistent wood species
• Higher dot gain on recycled uncoated papers, the more open, porous structure of recycled uncoated paper absorbs ink faster and spreads dots more than virgin uncoated

When to specify recycled paper

• Sustainability-focused communications where the tactile and visual cues of recycled paper (cream tint, visible fibre content) are part of the brand message, environmental reports, organic product packaging, heritage brand stationery
• Economy secondary packaging where print quality is not the priority
• Internal documents and economy printing where whiteness and surface quality are not critical
• Not recommended: premium brochures with photography, pharmaceutical packaging, food primary packaging, or any application requiring consistent colour reproduction or regulatory-grade food safety compliance

India is a significant paper producer with approximately 750–800 paper mills of varying scale. The domestic paper industry produces a wide range of grades, from newsprint and packaging paper to coated art and specialty papers. However, premium coated art paper for commercial print in India is predominantly imported, from Europe (Finland, Germany, Sweden, Austria) and increasingly from East Asia (Japan, South Korea, China).

What Indian mills produce well

• Uncoated offset paper, maplitho, bond, and writing papers. Indian mills produce competitive quality uncoated papers for letterheads, forms, books, and economy brochures.
• Packaging board, duplex board, kraft board, and economy SBS/FBB. The large-volume packaging grades are well-served by domestic mills.
• Newsprint, significant domestic production.
• Speciality papers, tissue, security paper (for some applications), and industrial papers.

Where imported paper is typically superior

• Premium coated art paper for brochures and catalogues, European mills (Sappi, UPM, Stora Enso, Mondi) produce coated art papers with tighter GSM tolerances, higher whiteness, and more consistent surface quality than most domestic equivalents
• Premium SBS board for cosmetics and pharma packaging, European and East Asian SBS boards consistently outperform domestic alternatives on surface smoothness and caliper consistency
• Specialty uncoated papers, premium writing papers, cotton papers, and textured stocks are almost exclusively imported

The certification landscape · FSC, PEFC, and BIS

• FSC (Forest Stewardship Council), the internationally recognised standard for responsibly sourced wood. FSC certification on a paper or board means the wood fibre comes from forests managed to social and environmental standards. Major international brands increasingly require FSC-certified packaging from their suppliers. Several Indian mills now hold FSC certification.
• PEFC (Programme for the Endorsement of Forest Certification), the European equivalent of FSC, widely recognised for timber and paper from European mills.
• BIS (Bureau of Indian Standards), Indian paper standards are defined by BIS IS codes. Key standards: IS 1848 (printing and writing paper), IS 14388 (paperboard for packaging). Familiarity with BIS specifications is useful for government and institutional procurement.