The Chemistry of Sizing: Understanding Moisture and Grease Resistance

Butcher paper is a durable, relatively coarse-grained kraft paper commonly used for wrapping fresh meats, hot smoked barbecue, deli counter applications, and general food service tasks. Its distinguishing functional property is a carefully engineered balance between liquid resistance and breathability. This balance is achieved during manufacturing through the controlled use of sizing agents and wet strength chemistries; together these treatments reduce water and fat penetration while preserving pore structure so moisture and air can still move through the sheet.

Manufacturing overview and where sizing is applied

Production begins with pulping and refining of predominantly long-fiber (softwood) kraft pulp to deliver the tensile and tear strength required for handling and wrapping. During the wet-end stage of the paper machine, additives including internal sizing agents, fillers, and wet-strength resins are introduced into the furnish. The web is then formed, pressed, dried, and often surface-treated or lightly calendered to adjust smoothness and porosity. Sizing can be applied internally (added to the furnish) and/or at the surface (surface sizing) depending on the performance profile desired.

How sizing chemistry works

At a basic level, sizing reduces a paper’s affinity for water and oils by depositing chemicals that alter the surface energy of the cellulose fibers or by forming barriers across fiber intersections. There are two common approaches:

• Internal sizing: Hydrophobic molecules such as alkyl ketene dimer (AKD) or alkenyl succinic anhydride (ASA) are emulsified and added into the pulp slurry. These agents adsorb to fibers and, during drying, react or orient to present hydrophobic groups at the fiber surface. The result is reduced capillary uptake of water without a continuous film across the sheet, so air permeability and vapour exchange are largely retained.
• Surface sizing and coatings: Surface-applied materials (starch, polyvinyl alcohol, or bespoke food-safe polymers) can reduce surface porosity and improve printability and grease resistance. Surface coatings that fully seal pores, such as polyethylene extrusion coating, produce high moisture and grease barriers but also remove the breathability that makes butcher paper valuable for certain food uses.

Wet strength and leak resistance

Wet strength is provided by adding resins—commonly polyamine-epichlorohydrin (PAE) or alternative crosslinking agents—so that fiber bonds remain intact when the paper is wet. In butcher paper, moderate wet strength prevents tearing or leaking of juices during handling without rendering the paper excessively stiff or non-breathable. Leak resistance is the practical outcome of combining hydrophobic sizing with appropriate wet strength: liquids are less likely to pass through or weaken the structure, but vapour and some moisture exchange continue.

Grease resistance: methods and trade-offs

Grease (lipid) resistance is technically different from water resistance because oils penetrate cellulose more readily. Historically, fluorochemical repellents provided excellent oil and water repellency, but due to regulatory and environmental concerns many producers now avoid PFAS for food-contact papers. Alternatives include:

• Organic hydrophobes (AKD/ASA) used at optimized dosages to limit oil uptake without full pore blockage.
• Surface-applied, food-safe polymers or modified starches that selectively reduce surface wettability to fats while maintaining bulk porosity.
• Beating and refining choices: tighter fiber bonding and controlled calendaring can reduce pore size enough to slow oil migration without eliminating air flow—this is a mechanical rather than chemical approach.

Note that full greaseproof papers (glassine or polyethylene-coated sheets) are unsuitable where breathability is required; butcher paper typically aims for moderate grease resistance so external surfaces do not stain or leak excessively while allowing internal moisture release.

Maintaining breathability

Breathability in butcher paper depends on porosity, pore size distribution, and the absence of continuous impermeable films. Manufacturers achieve this by carefully controlling the type and dosage of sizing agents (favoring internal sizing for minimal pore-filling), limiting surface coating add-ons, and optimizing machine drying and calendering so the sheet’s microstructure remains open. Testing for air permeability (e.g., Gurley or Bendtsen methods) and water absorbency (Cobb test) helps set process targets that match end-use needs.

Regulatory and food-safety considerations

Any chemical used in food-contact paper must meet relevant food-safety regulations (e.g., FDA, EU food contact lists) and be free from objectionable odors or flavors. Because of consumer and regulator scrutiny, many producers emphasize non-fluorinated chemistries and certified migration testing to ensure no harmful residues transfer to food.

Practical examples and end-use trade-offs

In barbecue and meat retailing, butcher paper is preferred over foil when smoke penetration and bark formation are desired: foil creates an impermeable barrier that traps moisture and inhibits smoke transfer, while butcher paper lets steam and volatile smoke compounds move, producing drier surface textures and richer smoked flavor. For takeaway applications where juices must be contained, some suppliers use a heavier-basis-weight butcher paper with slightly higher sizing and wet-strength or add a thin food-safe polyethylene layer only to the inner face to combine containment with an outer breathable surface.

Common mistakes in specification and production

• Over-sizing or heavy coating that eliminates breathability and undermines the product’s functional advantages.
• Choosing inappropriate sizing chemistries that react poorly with filler or recycled fibers, causing sizing reversion or poor performance.
• Neglecting regulatory compliance—using non-approved additives or failing migration tests for food contact.
• Failing to match wet-strength levels to end-use, resulting in either brittle, non-flexible sheets or weak products that leak during handling.

Summary

Butcher paper achieves its characteristic combination of moisture and grease resistance with breathability through carefully dosed internal sizing, selective surface treatments, and moderate wet-strength chemistries. The manufacturing goal is to reduce liquid uptake and prevent leaks while preserving pore structure for vapour and airflow—delivering a functional, food-safe material that performs in meat wrapping, smoking, and retail contexts.