Mục lục
Reviewed and updated by ICD - Week 24/2026
Quick summary:
- A container dunnage bag is built from three specialized materials: a load-bearing outer shell, an air-holding inner bladder, and a valve.
- Outer shell: multi-ply kraft (economical, mild moisture resistance, Level 1-3) or woven PP (very high load, reusable, Level 3-5).
- Inner bladder: a PA/PE composite film - PA is the gas barrier that holds pressure, PE adds toughness and heat-sealing.
- Valve: load-bearing PE/PP or nylon, with a fast type that optimizes inflation speed and holds working pressure.
The 3 materials of a container dunnage bag
A dunnage bag is a high-engineering product whose multi-layer structure resists compression, abrasion and impact over a long voyage. For the full layer breakdown, see structure and types; here we focus on the materials themselves.
Outer shell: strength and abrasion resistance
The outer shell touches the goods and container wall and sets the bag’s AAR level.
| Material | Traits | Load & use |
|---|---|---|
| Kraft paper | 2-6 plies, PP-laminated for moisture and friction | Level 1-3. Medium loads, square boxes. More plies = better static compression. |
| Woven PP | Cross-woven, dense, waterproof, very high tensile strength | Level 3-5. Very heavy, sharp-edged, reusable. |
Kraft paper is favored for economy and its natural friction (the bag does not slip), but it resists moisture less well; in humid sea transport its strength can drop slightly. The outer PP lamination limits water absorption and stops fiber tearing under high compression, keeping the bag intact. See what kraft paper is.
Woven PP is optimal for heavy loads with high impact and abrasion risk. Its cross-weave spreads shear force and resists tearing extremely well, making it the only material that survives rail shunting without failing. Its tensile strength is many times that of kraft, so the bag does not over-deform under large dynamic compression. See what woven PP fabric is.
Inner bladder: air retention
This layer seals the compressed air and holds the static pressure for the whole journey. It is usually a PA/PE composite film:
- PA (polyamide): the key gas barrier - air molecules (nitrogen, oxygen) diffuse through it very slowly, so the bag keeps stable pressure even as container temperature changes, preventing slow deflation over a 4-8 week voyage.
- PE (polyethylene): adds toughness and good heat-sealing - it takes the tension of inflation and impact without tearing, and forms the heat seal that closes the bag.
The PA/PE film thickness directly affects lifespan and pressure retention - thicker film resists gas diffusion and pressure differences better - and the heat-seal quality matters as much as the material.
Valve: pressure and speed control
The valve is high-grade engineering plastic (load-bearing PE/PP or nylon) that withstands continuous pressure and container temperatures. A fast valve (20-30 mm) inflates 2-3x faster and auto-locks; an internal rubber gasket gives the leak-free seal. See the dunnage bag valve guide.
Frequently Asked Questions (FAQ)
What is the inner bladder made of?
A PA/PE composite film. PA is the gas barrier that holds pressure; PE adds toughness and the heat seal.
Why does kraft need a PP lamination?
To limit moisture absorption and stop fiber tearing under high compression, keeping the bag intact in humid transport.
Which material reaches the highest AAR level?
Woven PP - its tensile and tear strength let it reach Level 3-5, the only material that survives rail shunting.
What is the valve made of?
Load-bearing PE/PP or nylon with a rubber gasket, resistant to ageing and container temperatures from -20C to 50C.
Contact ICD Viet Nam
For dunnage bags in the right material for your cargo, contact our team for a quote.
- Northern Vietnam: 0983 797 186 / 090 345 9186 / 090 5859 186
- Southern Vietnam: 098 6784 186
- Email: sales@icdvietnam.com.vn
- Zalo: Chat on Zalo
