How barrier coatings help paper packaging achieve moisture, grease, and oxygen resistance

As demand for fibre-based packaging continues to grow, one challenge remains: how can paper-based materials deliver the barrier performance required for modern packaging applications?

Paper and board packaging continue to gain momentum as brands seek out alternatives to plastic. However, paper does have inherent limitations. Cellulose fibres are intrinsically hydrophilic, and the porous capillary network within paper and board enables the rapid uptake and transmission of water, oils, and gases unless that structure is modified or sealed. 

Barrier coatings like those in the DecaCode range help bridge that functional gap. Rather than changing the bulk substrate, these coatings engineer the surface and near-surface layer of the paper to reduce wetting, pore penetration, and permeation. In doing so, they help paper-based packaging achieve the performance needed for many modern packaging applications while supporting fibre-led design objectives.

What are barrier coatings?

Barrier coatings are functional polymers or bio-based materials applied to paper and board substrates to enhance resistance to external influences. In practical terms, they form a continuous film that reduces the passage of liquids, vapours, gases, grease, and aroma compounds through the substrate. They are commonly used in applications such as takeaway food packaging, frozen food cartons, paper cups, bakery packaging, and grease-resistant wraps, where product protection is essential.

Why paper needs help with barrier performance

Paper is composed of a network of cellulose fibres with voids between them, which creates pathways for liquid uptake and gas transmission. Water interacts readily with paper, so any moisture exposure can rapidly lower packaging’s strength and lead to higher deformation or compromised integrity.

That same porous structure also permits grease and gas migration. In food packaging, this can mean oil staining, loss of appearance, and faster oxidation of sensitive contents. Aroma transfer is another issue, because volatile compounds can diffuse through an untreated fibre network more easily than through a tailored barrier layer.

How barrier coatings work

Most barrier coatings work by reducing surface wetting and filling or sealing the micro- and nano-scale voids in the paper structure. Once applied, the coating forms a continuous film that reduces capillary wicking and lowers permeability by creating a longer and more challenging diffusion path for migrating molecules.

For water-based systems such as DecaCode, the coating is typically a polymer dispersion in water. During drying, water evaporates, allowing the polymer particles to form a continuous film.  Additional formulation components or additives are then used to optimise barrier performance for specific barrier requirements. 

Barrier functions and measurement

Different barrier properties are measured in different ways because each transport mechanism behaves differently.

Water resistance is assessed through Cobb testing, which measures water absorptivity, and contact angle analysis, which indicates how readily a liquid spreads on the surface. A higher contact angle generally suggests a more water-repellent surface.

Grease resistance is typically evaluated using standardised KIT tests, which assess a coating's ability to resist oils and grease of varying aggressiveness. Performance depends on both the surface chemistry of the coating and its ability to seal the paper structure, helping prevent oil penetration into the substrate.

Moisture vapour resistance is usually expressed through water vapour transmission rate, or WVTR. This testing considers hydrophobicity, film continuity, and polymer density because water vapour can diffuse through coatings even when liquid water cannot.

Oxygen barrier performance is commonly assessed using oxygen transmission rate (OTR) testing.  Oxygen barrier performance can be sensitive to humidity, as many polymer systems become more permeable as relative humidity increases.

Sustainability and chemistry choices

Historically, barrier performance has often been achieved using polyethylene laminations, plastic films, or foil-based structures. While these can be highly effective, they also introduce complexity to recycling systems by adding mixed materials to a fibre-based pack.

Water-based barrier coatings offer a different route by preserving a fibre-led structure while adding the needed surface functionality. This can support more recyclable packaging designs, depending on the local recycling system and pack configuration.

Chemistry selection is now a major part of the sustainability discussion. Some barrier solutions have traditionally relied on fluorinated chemistries, including PFAS, to achieve oil and grease resistance because fluorinated groups are exceptionally effective at lowering surface energy. However, PFAS are under increasing regulatory scrutiny due to their persistence, bioaccumulation concerns, and the difficulty of managing them throughout product life cycles.

That is why PFAS-free, PTFE-free barrier technologies are increasingly gaining attention. Such solutions offer brands and converters an invaluable tool for both removing a substance of concern as well as maintaining barrier performance. DecaCode barrier coatings are formulated without added PFAS or PTFE, aligning with this shift in regulatory and market requirements and reflecting a broader industry transition towards safer and more sustainable material solutions. 

Enabling the next generation of paper packaging

Barrier coatings represent a key enabling technology in the evolution of paper-based packaging. By delivering resistance to moisture, grease, and gases, they enable fibre-based materials to meet the functional demands of modern packaging applications.

At the same time, advances in coating chemistry are supporting the development of packaging designs that align with recyclability goals and emerging regulatory expectations. Innovations such as DecaCode demonstrate how performance and sustainability can increasingly go hand in hand, helping converters and brand owners transition towards more circular packaging systems.

To find out more about barrier coating chemistry or explore the DecaCode range, visit www.flintgrp.com/products/flexography/inks-paper-board-eu/decacode/