Dunnage Bag Materials: Kraft, Woven PP and PA/PE Film

Reviewed and updated by ICD - Week 44/2026

Key takeaways

Container dunnage bags are made from three groups of material: an outer shell of plastic-laminated Kraft paper or woven PP fabric to carry the load, an air-holding liner of PA and PE laminated film, and a plastic valve with a locking cap. According to ICD Vietnam documentation, the liner is 75 micron PA film, the woven PP shell is 70 g/m² and the laminated Kraft paper is 65 g/m². The PA layer decides how long the bag holds air: in a 2024 study, a 79 micron PA/PE laminated film let about 60 times less oxygen through than a 92 micron PE film.

The article analyses the role of each material: Kraft paper (economical, moderate moisture limitation), woven PP fabric (durable, better puncture resistance, reusable) and PA/PE film (holds the air). The later sections show how to choose materials by cargo type, how to read a material data sheet when you enquire, and why the pressure in the bag rises when the container heats up.

I am Le Van Thang, and I have worked in packaging supplies at ICD Vietnam since 2011. The questions about materials I receive most are “can a paper bag survive sea transport” and “why do cheap bags leak air”. Both can be answered by the materials.

1. The standard 3-layer construction of a container dunnage bag

An industrial dunnage bag is a multi-layer technical product. Each layer does one job: the outer shell takes compression force and resists abrasion, the inner liner holds the air, and the valve controls inflation and release. If one layer fails, the bag is useless, so when comparing two bags, compare each layer, not just the price.

1.1. The outer layer: load-bearing and mechanical strength

The outer layer touches the cargo and the container wall directly, carrying compression strength and abrasion resistance. The shell material together with the bag size decides the working and burst pressure, and so the strength level of each bag code.

Kraft paper is popular for its economical price and good friction surface, which keeps the bag from sliding when placed between two units. The weak point of paper is that it absorbs moisture: damp paper weakens mechanically, so the paper shell is laminated with plastic film to limit water vapour. The laminated film also keeps the paper fibres bonded when the bag is compressed, reducing fibre tearing at the bag edge.

Woven PP fabric is the choice for heavy loads with a risk of impact and abrasion. The woven structure spreads cutting force and limits how far a tear spreads, so a woven PP shell resists puncture better than paper. There is no rule that “paper is Level 1-2, woven PP is Level 3-5”: the ICD Vietnam catalogue grades woven PP bags from Level 0 to Level 5, and the level belongs to each bag code.

For a specific comparison, ask the seller for three shell figures: grammage (g/m²), tensile breaking force in the warp and weft directions (N), and the burst pressure of the bag. Two bags that both say “Kraft” can differ a lot in these three figures.

1.2. The inner bladder: holding the air and stabilising pressure

This is the layer that keeps the compressed air sealed (air tightness), deciding whether the bag is still taut when the container reaches the destination port. The usual material is a laminated film of PA (polyamide, also called nylon) and PE (polyethylene), usually co-extruded in several layers with a tie layer between PA and PE.

The role of PA: PA is the gas barrier layer. In the study by Sharmin et al. (2024), a 79 micron PA/PE laminated film had an oxygen transmission rate of about 26.7 mL/m²/day, while a 92 micron PE film had about 1,597 mL/m²/day, about 60 times more even though the PE film was thicker. An earlier study by Kamal et al. (1984) also showed that adding PA to PE cut the oxygen permeability of PE by 2.8 to 3.6 times. A liner of PE only therefore leaks air faster, even though it looks identical at inflation.

The weak point of PA is moisture: PA absorbs moisture, and when damp its gas barrier falls. A thesis at Brunel University records that the oxygen permeability of PA6 rises about 5 times as humidity goes from 0 to 100%. That is why bag liners usually sandwich PA between PE layers: PE blocks water vapour very well and keeps the inner PA layer dry.

The role of PE: PE is flexible, takes the tension of inflation and impact without tearing, and is also the main material of the heat seal that closes the bag. A poor seal is as common a leak point as thin film, so seal quality matters as much as material quality.

Thickness and construction: with the same kind of film, thicker film lets air out more slowly. The ICD Vietnam catalogue states a 75 micron PA film liner. When comparing bags, ask both the liner thickness and its composition (PA + PE or PE only).

1.3. The valve: controlling pressure and speed

The valve is fixed firmly to the liner, lets air in during inflation, keeps it in when the gun is removed and lets it out when unloading. The valve must withstand the handling force of inserting and removing the gun and the temperature changes in the port yard without cracking.

Quick-fill valve: the diagram in ICD Vietnam documentation compares a standard 10 mm valve with a 30 mm quick-fill valve, with an inflation time ratio of about 1:3. The valve has a self-sealing mechanism when the gun is removed and a screw cap for an extra layer of locking.

Safety mechanism: the self-sealing mechanism and a tightly screwed valve cap are two layers that hold the air. Leaving off the valve cap is one of the simplest mistakes that makes a bag go flat gradually while the vehicle is moving.

2. Classifying dunnage bags by material construction and use

The outer shell material creates a clear difference in load capacity and handling, which in turn affects how the load is secured.

2.1. Kraft paper dunnage bags

Suited to: cargo without sharp edges, square box-shaped loads, medium weight, where a low cost of blocking is needed. The usual choice is a Level 1 bag, working at about 0.2 bar according to the ICD Vietnam catalogue; higher levels are quoted by code.

Cost and risk: this is the economical choice for one-way transport, but it needs more careful blocking, always with a pad covering sharp edges. The paper shell tears easily on sharp edges and should not be reused many times.

Related product: Kraft paper dunnage bag

2.2. Woven PP dunnage bags

Suited to: heavy cargo such as machinery, steel coils and concentrated loads; cargo with sharp edges; cargo going by rail. The strength level is by code, from Level 0 to Level 5 in the ICD Vietnam catalogue.

Long-term economy: the initial price is higher but the bag can be reused if it is not torn and the valve is still sealed. In a closed supply chain where bags are recovered at the unloading point, reusing woven PP bags lowers the blocking cost. Note that the CTU Code uses a lower safety factor for reusable bags: 0.5 compared with 0.75 for single-use bags.

Moisture resistance: PP fabric does not absorb water like paper, so it suits long journeys through humid regions better, where condensation inside the container affects paper-based materials. That is an advantage over paper, not absolute moisture resistance: woven fabric has gaps between the threads, and the seams are also a place for water to get in.

2.3. Carton void-fill air bags

Suited to: small, fragile goods, filling the void inside a carton (e-commerce, cosmetics, glass), not inside a container. The material is thin, soft PE or LLDPE film. This type is inflated with a mini electric pump, not industrial compressed air, because the pressure is far too high.

How does container temperature affect a dunnage bag?

A container in the sun heats up very fast. According to the Container Handbook of the German Insurance Association (GDV), when it is 25-30 °C outside, the air in the upper part of the container can reach 50-55 °C. The air in the bag warms with it, and the pressure rises.

A simple estimate by the Gay-Lussac law (treating the bag volume as constant): a bag inflated to 0.2 bar at 20 °C, if heated to 55 °C, rises to about 0.34 bar. In reality the bag swells a little more so the pressure rises less, but it is still the reason not to over-inflate beyond the recommended level. A Level 1 paper bag bursts at about 0.6 bar according to the catalogue, so inflating to exactly 0.2 bar still leaves a margin; inflating to 0.4 bar and leaving the container in the sun is already close to the threshold.

Heat also affects the film: high temperature makes gas pass through the film faster. So for a long journey through hot regions, a liner with a PA layer and good seals matters even more.

3. Choosing materials and technical standards

Choosing the right material must go together with inflating to the right pressure and placing the bag in the right gap, so that the bag can deliver its full capability.

3.1. Material selection criteria

Cargo with sharp edges: prefer woven PP bags and still add an edge-covering pad. The woven shell resists tearing better than paper, lowering the risk of a punctured bag. With paper bags, a stiff board or honeycomb pad at sharp edges is mandatory.

Reuse requirement: choose woven PP bags and have a procedure to recover bags at the unloading point. Check the bag before every use: no tears, sealed valve, holds air overnight.

Humidity and transit time: on a long journey across hot, humid seas, a woven PP bag is safer than a paper bag. With paper bags, keep them dry before use and avoid loading wet goods into the container.

Cargo going by North American rail: needs a bag that meets the AAR level in General Information Bulletin No. 9 of the Association of American Railroads. For container cargo going by sea or road, the basis is the CTU Code and the bag manufacturer’s guidance.

3.2. Checking the material and the valve quality

Before buying, ask the supplier for the origin of the materials and quality test information:

• Figures printed on the bag: size, working pressure, burst pressure.
• Liner composition and thickness: PA + PE or PE only, how many microns.
• Outer shell: grammage (g/m²) and breaking force in warp and weft.
• Results of the drop test, tensile test and vibration test, and the test report from an inspection body if available.
• Valve type and compatible inflation gun.

The ICD Vietnam catalogue lists the drop, pull and vibration tests and the AAR, SGS and MSDS documents for dunnage bags. When you receive a test report from any supplier, check whether the report applies to the exact bag code and the right year.

Frequently asked questions about dunnage bag materials

Can the PA/PE liner withstand the high temperatures in a container?

Yes, under ordinary conditions. According to the GDV Container Handbook, the air in a container can reach 50-55 °C when it is 25-30 °C outside. What needs attention is that the pressure in the bag rises with temperature, so inflate to the recommended pressure and do not over-inflate.

Does a Kraft paper dunnage bag have a moisture-resistant layer?

Yes. The paper bag shell is plastic-laminated Kraft paper; the film layer limits moisture getting into the paper, helping the paper keep its strength in sea transport. It is a moisture-limiting layer, not absolute moisture protection, so keep bags in a dry place.

Do woven PP bags have a higher strength level than Kraft bags?

Not always. The ICD Vietnam catalogue grades woven PP bags from Level 0 to Level 5; the level belongs to each bag code. A woven PP shell has better tensile strength and puncture resistance than paper, so the high-level bag codes are usually woven PP bags.

Can woven PP material be recycled?

PP is a thermoplastic with recycling code number 5 and can be recycled. A dunnage bag is a composite material (PP fabric, PA/PE liner, valve), so recycling requires separating the parts. A woven PP bag that is still good should be reused before being sent for recycling.

What is the benefit of a quick-fill valve?

According to ICD Vietnam documentation, the 30 mm quick-fill valve inflates faster than the 10 mm standard valve, with an inflation time ratio of about 1:3. The valve has a self-sealing mechanism when the gun is removed and a screw cap for extra locking.

Are plastic component trays and carton void-fill air bags made of the same material?

Usually the same plastic family, PE or LLDPE, but with different thickness and purpose. Carton void-fill air bags use thin, soft PE/LLDPE film to make an air cushion; component trays use thicker plastic or stiffer PP so they can be stacked.

Contact us for technical advice and to buy

References

• TAPPI (Technical Association of the Pulp and Paper Industry) - Kraft paper and woven PP fabric materials used to make dunnage bags.
• Sharmin N. et al. (2024), Recyclable and non-recyclable packaging films with different barrier properties, PubMed Central PMC11673516.
• Kamal M.R. et al. (1984), Permeability of oxygen and water vapor through polyethylene/polyamide films, Polymer Engineering and Science
• Brunel University, thesis The blending and permeability of polymers
• GDV Container Handbook, section 10.3.2.1: the effect of solar radiation on container temperature.
• Wikipedia - Polypropylene
• IMO/ILO/UNECE CTU Code, MSC.1/Circ.1497.
• ICD Vietnam dunnage bag catalogue: 75 micron PA film, 70 g woven PP fabric, 65 g laminated Kraft paper, Levels 0-5, 10/30 mm valves.