Kraft Paper: Definition, Types, Manufacturing Process, and Benefits

Kraft paper is a high-strength paper produced by the kraft chemical pulping process and used for packaging across retail, industrial, and food-contact applications. It preserves long cellulose fibers, provides high tensile and tear resistance, and remains recyclable and biodegradable when uncoated. Five common types of kraft paper are natural brown (retail wrapping, corrugated facings), bleached (premium printed bags), sack (multiwall industrial sacks), coated (PE or clay for moisture or print control), and recycled (post-consumer or post-industrial blends for eco-branded mailers).

Production follows eight main stages that include wood preparation and kraft pulping; washing, screening, and chemical recovery; optional delignification or bleaching; stock preparation with sizing and wet‑strength additives; sheet formation, pressing, and drying; surface treatment, coating, and lamination; converting and finishing; and quality control and testing. Benefits of kraft paper are strength (multi-ply and wet‑strength for heavy loads), cost-efficiency (single- or multi-ply tradeoffs), printability (flexo/offset and clay coatings), environmental performance (biodegradability and 30–100% recycled-content options), functional barriers (PE, wax, clay for moisture or grease resistance), and converting flexibility (valve forming, sewing, die-cutting). Principal uses cover five areas: retail presentation, industrial sacks, food packaging, protective cushioning/void fill, and corrugated facings and rollstock.

What is Kraft Paper?

Kraft paper is a strong paper made by chemically pulping wood via the kraft process, creating coarse, high-tensile sheets used for packaging. The term “kraft” means “strength” in German. The process strips lignin and preserves long cellulose fibers, producing paper with high tear resistance and good surface for printing.

Five common types: natural brown, bleached, sack, coated, and recycled.
Key attributes: high tensile strength, biodegradability, recyclability, and available calipers for light to heavy loads.
Primary uses: wrapping, retail bags, corrugated facings, industrial sacks, and protective cushioning for shipping.

What are the Properties of Kraft Paper?

Kraft paper has various properties, including high tensile strength, natural appearance, biodegradability, customizability, weight variability, and recyclability.

High Tensile Strength: Kraft paper can endure significant stress without tearing, making it suitable for heavy-duty packaging.
Natural Appearance: Its earthy brown color provides a rustic and eco-friendly aesthetic.
Biodegradability: Kraft paper decomposes naturally, reducing environmental impact.
Customizability: It can be printed, dyed, or laminated for branding purposes.
Weight Variability: Available in different thicknesses and weights, ranging from lightweight wrapping paper to heavy-duty industrial grades.
Recyclability: Kraft paper is highly recyclable, contributing to sustainable packaging practices.

What are the Types of Kraft Paper?

Kraft paper comes in various types, each tailored to specific applications. Below are the most common types:

1. Natural Brown Kraft Paper

Natural brown kraft paper is an unbleached, high-strength paper commonly supplied in 40–160 g/m² grades. It preserves long cellulose fibers from the kraft process, giving high tear resistance and a matte, absorbent surface suitable for many print methods such as flexography and offset. Typical uses include retail wrapping, shopping bags, corrugated facings, and interleaving.

Surface and Printing: uncoated; accepts water-based and soy inks, and can be waxed or oil-treated for limited grease resistance.
Weight Guidance: choose 40–80 g/m² for light wrapping, 90–140 g/m² for bags, and 140–160 g/m² for corrugated facings.
End-of-life: recyclable and compostable if uncoated; retains recyclability when unlaminated.

2. Bleached Kraft Paper

Bleached kraft paper is chemically whitened to provide a bright, smooth surface while retaining kraft strength. It offers higher brightness and improved print consistency compared with natural brown grades, which makes it suitable for high-visibility branding. Typical weight ranges from 50–180 g/m². Uses include premium shopping bags, cosmetic and apparel packaging, and printed wraps.

Surface and Finishing: compatible with clay/coating layers for gloss or matte finishes and with water-based barrier coatings for food contact, if produced to applicable food-safety standards.
Environmental Note: available in ECF (elemental chlorine-free) or TCF (totally chlorine-free) variants. Verify mill disclosures for bleaching chemistry and recycled-fiber content.

3. Sack Kraft Paper

Sack kraft paper is a heavy-duty grade engineered for multiwall and single-wall industrial sacks. Typical basis weights run 140–300 g/m² or higher in multi-ply constructions. It prioritizes burst strength, tear resistance, and seam integrity for bulk packaging. Uses of sack kraft paper are cement bags, flour and grain sacks, feed and fertilizer sacks.

Construction and Finishing: formed as single-ply or multi-ply sheets, sewn or valve-formed, and often paired with an internal polyethylene or mineral coating for moisture resistance.
Compliance: for food-contact sacks, use designated food-grade sack kraft produced on dedicated lines and certified per regional regulations.

4. Coated Kraft Paper

Coated kraft paper receives a functional layer, commonly polyethylene (PE) or clay, to add moisture, grease, or print-quality properties. Two common variants exist as PE-coated for liquid or moisture barriers and clay-coated for sharper printing and bright whites. Uses include food wrappers, moisture-resistant bags, liquid packaging pouches, and high-graphics sleeves.

Recycling Impact: plastic or polymer coatings reduce curbside recyclability; specify recyclable or easily separable coatings if end-of-life recovery matters.
Printability: clay-coating yields near-photographic print results with conventional CMYK processes.

5. Recycled Kraft Paper

Recycled kraft paper contains post-consumer or post-industrial fibers and is offered in 30–100% recycled-content grades depending on performance needs. Recycled content lowers brightness and, at high percentages, reduces tensile strength versus virgin kraft; manufacturers often blend recycled and virgin fibers to meet specific strength targets. Uses are secondary packaging, filler paper, eco-focused retail bags, and mailers.

Certification and Claims: specify percentage recycled content and use labels such as “FSC Recycled” where traceability is required.
Performance Tuning: increase ply count or add a virgin-fiber liner if recycled grades need added burst or tear resistance.

Selection guidance: choose kraft paper type by matching three parameters, such as basis weight (g/m²), surface treatment (coated/uncoated), and barrier needs (moisture/grease/food-contact). Examples: select 50–80 g/m² bleached kraft for printed retail bags; select 180–300 g/m² sack kraft for multiwall industrial sacks; avoid PE-laminated grades when curbside recycling is a priority.

How is Kraft Paper Manufactured?

Kraft paper is produced by chemically pulping wood to separate long cellulose fibers, forming wet sheets on a paper machine, then pressing, drying, and finishing; process branches (bleaching, coating, recycling, multi-ply) create the common kraft types.

The full manufacturing sequence is divided into discrete stages that determine strength, brightness, and end-use. Below are the main steps and the process choices that yield natural brown, bleached, sack, coated, and recycled kraft.

1. Wood Preparation and Pulping

Wood logs are debarked and reduced to chips sized for the digester. Chips enter the kraft digester, where sodium hydroxide and sodium sulfide break lignin at 150–170°C, producing brown kraft pulp with a typical yield of about 45–55% of dry wood.

2. Washing, Screening, and Chemical Recovery

After cooking, the pulp is washed and screened to remove knots and oversized rejects. Black liquor (dissolved lignin and chemicals) is concentrated and burned in a recovery boiler to reclaim inorganic chemicals and generate steam for mill power.

3. Delignification and Optional Bleaching

Mills apply oxygen delignification or peroxide/bleach stages when higher brightness is required. Choose no bleaching for natural brown kraft; use elemental-chlorine-free (ECF) or totally-chlorine-free (TCF) sequences for bleached kraft to meet brightness and regulatory needs.

4. Stock Preparation and Additives

Pulp is refined to adjust fiber fibrillation and strength. Additives include sizing agents (alkyl ketene dimer or rosin) for water resistance, fillers for surface smoothness, and wet-strength resins (polyamide-epichlorohydrin) for sack kraft where seam and burst resistance matter.

5. Sheet Formation, Pressing, and Drying

The stock forms on a Fourdrinier or cylinder machine. Wet webs pass through press felts to remove water, then through drying cylinders to reach the target grammage (g/m²). Calendering even thickness and adjusts surface gloss or smoothness.

6. Surface Treatment, Coating, and Lamination

Functional coatings add properties: clay or calcium carbonate coatings improve print quality; polyethylene (PE) or bio-based films add moisture and grease barriers. Wax or oil treatments provide temporary grease resistance for food wraps. Note: polymer layers reduce curbside recyclability unless designed for separation.

7. Converting and Finishing

Converted products include single- or multi-ply sacks, rolls for corrugated facings, printed retail bags, and liners. Converting operations include ply bonding, valve forming, sewing, pleating, die-cutting, and flexographic or offset printing. Basis-weight selection follows end-use: 40–160 g/m² for retail and facings; 140–300+ g/m² for sack grades.

8. Quality control and testing

Common QC tests measure grammage, tensile strength, tear resistance, burst strength, moisture content, and porosity. Mills use these metrics to match paper grade to application and to control consistency across production runs.

How process choices map to common kraft types

Natural brown kraft: skip bleaching as minimal surface treatment preserves strength and recyclability (examples: retail wraps, corrugated facings).
Bleached kraft: add bleaching stages and surface coatings for brightness and high-quality printing (examples: premium bags, cosmetic wraps).
Sack kraft: use heavier basis weights, wet-strength resins, and multi-ply bonding for seam integrity (examples: cement sacks, flour bags).
Coated kraft: apply clay or PE coatings for print fidelity or barrier function (examples: food wrappers, moisture-resistant pouches).
Recycled kraft: incorporate deinked post-consumer or post-industrial fibers with adjusted refining or ply count to recover strength (examples: filler paper, eco-branded bags).

Environmental controls like chemical recovery, closed-loop water treatment, and choice of bleaching chemistry affect a mill’s emissions and the recyclability of final products. Specify process criteria (bleaching type, recycled content, coatings) when selecting a kraft grade for your packaging.

What are the Benefits of Kraft Paper in Packaging?

Kraft paper delivers six practical benefits for packaging: strength, cost-efficiency, printability for branding, environmental performance, barrier and functional options, and converting flexibility.

Strength: high tensile and tear resistance across basis weights (40–300+ g/m²), suitable for heavy loads and abrasion-prone handling (examples: multiwall sacks, corrugated facings, industrial wraps).
Cost-efficiency: available as single-ply or multi-ply constructions to trade off material cost and performance, lowering per-unit packaging cost for bulk and retail runs (examples: commodity sacks, rollstock for corrugators).
Printability and branding: accepts flexographic, offset, and water-based inks; bleached and clay-coated grades improve color fidelity and white point for graphics (examples: shopping bags, printed sleeves, gift wraps).
Environmental performance: biodegradable and widely recyclable; offered in 30–100% recycled-content grades and certifiable via schemes like FSC Recycled (examples: eco-branded mailers, secondary packaging). Avoid PE-laminated grades if curbside recycling is a priority.
Barrier and functional options: supports coatings and treatments—PE lamination for moisture, clay coating for print, wax/oil for grease, wet-strength resins for seam integrity—enabling food-contact and industrial uses (examples: food wrappers, moisture-resistant pouches, cement sacks). Note: polymer layers reduce curbside recyclability.
Converting flexibility: compatible with pleating, valve forming, sewing, die-cutting, and ply bonding; mills can tune fiber blends and calendering to meet runnability and machinability targets (examples: sewn sacks, die-cut retail boxes, printed rollstock).

Many different types of kraft paper exist; choose by basis weight, surface treatment, and recycled content to match package strength, print needs, and end-of-life expectations. Kraft paper benefits, such as strength, printability, recyclability, functional coatings, and convertibility, cover most packaging requirements.

What are the uses of Kraft Paper in Packaging?

Kraft paper serves five principal packaging uses: retail presentation, industrial sacks, food-contact wraps, protective cushioning/void-fill, and corrugated facings and rollstock.

Retail packaging: shopping bags, gift boxes, and printed sleeves; use bleached or clay-coated kraft for high-fidelity graphics (50–140 g/m²) and natural brown kraft for rustic branding (40–120 g/m²). Specify surface treatment (clay, varnish) for color fidelity and handle reinforcement or multi-ply for bag load capacity.
Industrial sacks: cement bags, flour sacks, and feed sacks; use sack kraft in single- or multi-ply constructions at 140–300+ g/m² with wet‑strength resin and sewn or valve closures. Add an internal polyethylene or mineral coating if moisture protection is required.
Food packaging: bakery wraps, butcher paper, takeout pouches, and grease‑resistant liners; use PE‑coated kraft or wax/oil‑treated kraft for moisture and grease barriers, and choose food‑grade certified grades for direct contact. Use clay‑coated bleached kraft for printed food labels if bright whites are required.
Protective packaging: crumple-wrap, interleaving sheets, and padded mailers; use low-to-mid basis weights (40–100 g/m²) for cushioning and void fill, and use recycled kraft for inexpensive filler paper. For fragile items, combine kraft wrap with corrugated pads or bubble layers to meet drop-test requirements.
Corrugated facings and rollstock: linerboard, corrugator rolls, and inner facings for boxes and trays; use higher-basis kraft (80–160 g/m²) for single-face and linerboard applications. Select natural brown kraft for strength and recyclability; choose bleached or coated facing where product presentation or print contrast is prioritized.

Selection rules: match basis weight (g/m²), surface treatment (uncoated, clay, PE, wax), and recycled content to the use case. Use multi-ply or add wet‑strength resins if seam integrity or burst resistance is required. Avoid PE‑lamination if curbside recyclability is a priority.

Conversion and print notes: specify flexographic or offset printing, handle types, ply bonding, and valve/seam options during order. For eco claims, state the percentage of recycled content and any certifications (for example, “FSC Recycled 100%”), and verify that chosen coatings do not breach those claims.