Types and Materials of Inner Liners: How to Choose the Right Liner

Choosing an Inner Liner starts with understanding the product’s vulnerabilities and the supply chain conditions it will face. Different liner types deliver different combinations of barrier performance, mechanical strength, chemical resistance, and cost. This article walks beginners through the most common materials, typical use cases, and selection criteria so you can match liner performance to real-world needs.

Common inner liner materials and where they’re used:

• Low-density polyethylene (LDPE): Soft, flexible, and low-cost. Widely used as bag liners inside boxes, pails, and drums. Good moisture barrier and puncture resistance for many non-reactive products like grains, powders, and textiles.
• High-density polyethylene (HDPE): Stiffer and tougher than LDPE. Used for drum liners, heavy-duty sacks, and some chemical applications where increased puncture and tear resistance are required.
• Co-extruded films: Multiple layers of different resins are extruded together to combine properties — for example, an inner sealable layer, a strong structural layer, and an outer tough layer. Co-extrusion enables tailored performance like better puncture resistance or improved barrier while keeping costs reasonable.
• Metallized film and foil laminates: For products sensitive to oxygen, light, or aromas (snacks, coffee, pharmaceuticals), metallized PET or aluminum foil laminates provide excellent barrier properties. They’re commonly used for pouches and inner liners that require long shelf life.
• EVOH and Nylon (PA) laminates: These offer high oxygen barrier (EVOH) and puncture resistance (nylon). They’re common in multi-layer food packaging where oxygen and aroma control are vital.
• Paper and kraft liners: In corrugated board, inner liner often refers to linerboard — typically kraft or test liner. These provide structural support and a printable surface but offer little moisture barrier unless coated or combined with a film liner.
• Specialty liners (anti-static, chemical-resistant, breathable): Anti-static liners add dissipative properties for flammable solvents or sensitive electronics. Permeable liners are used for produce or materials needing controlled respiration.

Material properties that matter when selecting an inner liner:

• Barrier performance: Measured by metrics like WVTR (water vapor transmission rate) and OTR (oxygen transmission rate). Choose low WVTR/OTR liners for moisture- and oxygen-sensitive products.
• Puncture and tear resistance: Important for sharp or heavy contents and for automated filling lines.
• Sealability: Heat-sealable layers are essential when you need hermetic seals for freshness or spill prevention.
• Chemical compatibility: Ensure liners won’t react with or leach into the product. Food and pharma require certified food-contact materials; chemicals may need liners resistant to solvents or acids.
• Temperature tolerance: Consider hot-fill, cold-chain, and sterilization processes. Some liners withstand pasteurization or freezing better than others.
• Static control: Static-dissipative liners are required when handling flammable solvents or electronic components.

How thickness and construction affect performance:

• Thickness is usually specified in microns (µm) or mils. Thicker films generally offer better puncture resistance and lower permeability but increase cost and may affect sealability.
• Multi-layer or co-extruded constructions let manufacturers combine a thin barrier layer (like EVOH) with a protective outer layer — delivering performance similar to thicker single-layer films at lower weight.

Practical selection checklist for an Inner Liner:

1. Identify the product’s sensitivity: moisture, oxygen, light, contamination, chemical reactivity, or static risk.
2. Consider regulatory requirements: food-contact approvals (FDA, EU), pharmaceutical standards, or hazardous material restrictions.
3. Account for the supply chain: duration of transit, likelihood of rough handling, and temperature extremes.
4. Decide on single-use vs. reusable: single-use liners improve sanitation; reusable solutions can be more sustainable but need cleaning and inspection protocols.
5. Balance cost and performance: choose the minimal specification that reliably protects the product while controlling costs.

Real examples to help you choose:

• Snack manufacturer: Metallized PET or aluminum foil liner to block oxygen and light, preserving crispness and flavor. Heat-sealable laminated films provide a hermetic seal in flexible pouches.
• Chemical exporter: HDPE drum liners with anti-static additive to reduce ignition risk and provide strong chemical resistance for solvent transport.
• Whiteboard paper rolls shipped in corrugated cores: Use kraft inner linerboard for structural support, and add a thin LDPE film liner if moisture protection is needed in humid climates.

Environmental and sustainability considerations:

• Multi-layer films often can’t be recycled easily because layers are different plastics. Look for mono-material solutions where possible or suppliers offering take-back and recycling programs.
• Consider lighter gauge films that maintain barrier using advanced polymer technology to reduce material use and transport emissions.

Conclusion: selecting the right Inner Liner is a balance of protection, compliance, handling, cost, and sustainability. Start by defining the product’s vulnerabilities and the conditions it will face in the supply chain, then match those needs to liner materials and constructions. Consulting with liner suppliers and testing with real-world filling and shipping scenarios is a good practice before committing to large runs.