Kraft paper is among the most mechanically strong paper materials produced at industrial scale. Its name comes from the German word for strength (Kraft), reflecting the pulping chemistry that produces long, intact cellulose fibres. These fibres give kraft paper its characteristic tear resistance and its suitability for packaging applications where structural integrity matters.
Within the broader discussion of sustainable packaging materials, kraft paper occupies a specific position: it is renewable, recyclable in most municipal systems, compatible with composting in uncoated form, and produced through a process that has improved considerably in resource efficiency over recent decades.
The Sulphate Pulping Process
Kraft paper is produced from sulphate pulp, also called kraft pulp. In the kraft process, wood chips are cooked under pressure in an alkaline solution of sodium hydroxide and sodium sulphide. This chemical mixture breaks down the lignin that holds cellulose fibres together in wood, releasing the fibres while preserving their length and structural integrity to a greater degree than acid-based pulping methods.
The resulting pulp can be left unbleached — retaining a brown colour from residual lignin — or bleached to produce white kraft grades used in higher-purity applications. Unbleached kraft is used for bags, sacks, and corrugated board liner; bleached kraft goes into food-contact packaging, medical packaging, and white carton board.
Chemical Recovery in the Kraft Process
A distinctive feature of the sulphate process is its chemical recovery loop. The cooking liquor containing dissolved lignin is concentrated and burned in a recovery boiler, generating both energy and a smelt from which the process chemicals are regenerated. This closed-loop approach makes the kraft process one of the more resource-efficient chemical pulping methods and enables mills to be largely self-sufficient in heat energy.
Material Properties Relevant to Packaging
The long fibre length produced by the kraft process translates into high tensile strength and burst resistance in the finished paper. This is the property that makes kraft paper suitable for multi-wall sacks carrying heavy products like cement, flour, or animal feed, as well as for carrier bags expected to carry significant loads.
Key material characteristics of kraft paper include:
- Tensile strength: Higher than sulphite or groundwood paper at equivalent grammage, due to longer, less damaged fibres.
- Porosity: Unbleached kraft has relatively high porosity, which is relevant for applications where breathability is required (e.g. valve sacks for powders).
- Moisture sensitivity: Uncoated kraft paper absorbs moisture and loses strength when wet. This limits its direct use in wet or humid environments unless treated or laminated.
- Recyclability: Uncoated, unlaminated kraft paper is accepted in standard paper recycling streams and falls within EN 643 Group 4 grades. Coatings, laminates, and adhesive applications can complicate recyclability.
Kraft Paper in the Context of the EU Single-Use Plastics Directive
The EU's Single-Use Plastics Directive (SUPD), adopted in 2019 and progressively implemented in member states including Poland, restricts or bans certain single-use plastic items and requires manufacturers to move towards alternatives. Paper-based alternatives, including kraft paper bags, have been adopted across retail and food-service sectors partly in response to these restrictions.
However, the environmental case for paper versus plastic is not straightforward. Life-cycle assessments comparing paper and plastic bags consistently find that paper bags require more energy and water to produce and generate more production waste per unit. The advantage of paper becomes clearer when end-of-life is considered: paper degrades in natural environments, is compatible with composting, and is recycled at higher rates than plastic film in most European collection systems.
This complexity is worth noting because packaging sustainability claims that cite material substitution without considering the full production cycle can be misleading. The EU's Packaging and Packaging Waste Regulation (PPWR), currently in legislative revision, is expected to introduce minimum recycled content requirements and recyclability criteria that will shape material selection decisions beyond simple plastic-versus-paper comparisons.
Grammage Ranges and Applications
Kraft paper is produced across a wide grammage range, roughly from 40 gsm to 150 gsm for standard packaging applications, with heavier boards produced for corrugated liner and carton stock. Grammage selection in packaging design is driven by load requirements, printing specifications, and regulatory requirements for food-contact applications.
| Grammage range | Typical application |
|---|---|
| 40–60 gsm | Interleaving, lightweight wrapping |
| 60–90 gsm | Retail carrier bags, wrapping paper |
| 90–120 gsm | Heavy-duty bags, e-commerce mailers |
| 120–150 gsm | Multi-wall sacks, industrial bags |
| 150 gsm+ | Corrugated liner, carton board |
Kraft Paper Production in Poland
Poland has a domestic paper and board manufacturing sector that includes mills producing kraft-based materials. The country's forest resource and its access to recycled fibre streams from corrugated collections support both virgin and recovered fibre-based production. Several Polish mills operate as part of European groups and supply packaging materials to domestic and export markets.
Corrugated board — which uses kraft-grade liner and fluting medium — is one of the major output categories for the Polish paper industry. The growth of e-commerce and changing retail packaging requirements have maintained demand for corrugated materials at a substantial level in recent years.
References
- CEPI — Confederation of European Paper Industries
- EU Single-Use Plastics Directive 2019/904 — EUR-Lex
- European Commission — Proposal for Regulation on Packaging and Packaging Waste (PPWR)
- Two Sides — Paper and Packaging Sustainability Data