Mục lục
Reviewed and updated by ICD - Week 24/2026
Quick summary:
- A dunnage (load-securing) bag is an essential void-fill solution built from three specialized layers: a load-bearing outer shell, an air-holding inner bladder, and a fast-inflation valve.
- The outer shell material decides the bag’s AAR level: kraft paper (economical, mild moisture resistance) for Level 1-3, and woven PP (very high load, reusable) for Level 3-5.
- Bags are classified by AAR level (1-5) and by use: container load bracing, sharp-edged goods, and in-box shock protection.
- The fast-inflation valve is key to filling speed and to holding the correct working pressure.
The standard 3-layer structure of a container dunnage bag
A container dunnage bag is an engineered tool designed to absorb large compression and strong shunting forces. Its construction follows a multi-layer principle that maximizes strength and air retention. The three layers each do a distinct job.
Outer layer: strength and mechanical durability
This layer touches the goods and the container wall and bears the main job of resisting compression, abrasion and tearing. Its material directly sets the bag’s AAR level.
| Material | Technical traits | Load level & use |
|---|---|---|
| Kraft paper | 2-6 plies of kraft, pressed and PP-laminated (Kraft-PPW) for moisture resistance | Level 1-3. Medium loads, square pallets, low cost. More plies = higher level. |
| Woven PP | Cross-woven polypropylene, high density, waterproof, very high tensile strength | Level 3-5. Tear and puncture resistant. Required for sharp-edged, very heavy, reusable loads. |
The number of kraft plies or the use of woven PP decides how much dynamic compression the bag absorbs without tearing. Woven PP is superior because it handles extreme shunting forces that kraft cannot. See our detailed guide on kraft paper types.
Inner bladder: air retention and pressure stability
This is the air chamber, and it is the most important layer for holding steady pressure so the bag does not deflate on a long journey. The material is usually a PA/PE composite film: the PA (polyamide) layer is an excellent gas barrier that stops compressed air escaping, while the PE (polyethylene) layer adds toughness and good heat-sealing. If this layer leaks, static compression drops and the bag loses its ability to secure the load.
Valve: speed and safety control
The valve decides operating efficiency and pressure accuracy. A large-diameter fast valve (20-30 mm) cuts inflation time to about one third of an old-style valve. It has an automatic air-lock the moment the inflation gun is withdrawn, then the cap is tightened for a complete seal. Fast inflation optimizes loading and unloading time at the port - a major economic factor in logistics.
Detailed classification of dunnage bags
Kraft paper bags (Level 1-3): the standard economical solution
These hold the largest market share thanks to low cost and good performance in normal conditions, used for road and domestic sea container transport. They typically reach Level 1 or 2 AAR - enough to resist dynamic compression (sideways sway, hard braking) in light to medium transport. Used for FMCG, cartons and packaging. Limitation: lower mechanical strength than woven PP, prone to tearing on sharp edges, and not suited to repeated reuse.
Woven PP bags (Level 3-5): heavy-duty and reusable
The woven PP shell gives superior mechanical strength and tensile resistance, and the cross-weave spreads shear force better than kraft. It reaches Level 3 to 5 AAR and is required for rail transport (against shunting forces) and very heavy loads (over 25 tonnes per container). It is 2-3 times more tear and puncture resistant than kraft and is fully waterproof, protecting the bag on long sea voyages.
In-box air bags (PE/LLDPE): shock protection and small void fill
These are small, low-pressure, soft air bags used to cushion and fill gaps between individual products inside a carton (e-commerce, cosmetics, glassware). Made of thin, light PE or LLDPE, they carry no AAR level because they do not secure a container load, and they are inflated with a mini electric pump rather than industrial compressed air.
Key technical criteria: pressure and size
Working pressure and compression
Working pressure (usually 0.2 bar) is the level needed for the bag to create optimal static compression, turning loose cargo into one unified block. Under-inflate, and the bag cannot push back against dynamic forces on impact. Always inflate with a pressure-gauge gun to avoid over-pressure (burst risk) or under-pressure (weak force).
Maximum void principle
Every bag size has a maximum void it can safely fill. Exceeding that gap leaves the bag over-stretched and unable to brace the load reliably. Choosing the right bag size for the actual gap is as important as choosing the right material level.
Frequently Asked Questions (FAQ)
Kraft or woven PP - which should I choose?
Choose kraft for medium loads and square pallets where cost matters. Choose woven PP for sharp-edged goods, very heavy loads (25+ tonnes), rail transport, or when you need to reuse the bag.
What does the AAR level mean?
AAR levels (1-5) rate how much dynamic compression the bag absorbs. Higher levels use more kraft plies or woven PP to withstand greater impact.
What working pressure should I inflate to?
Typically 0.2 bar, set with a gauge gun. Under-inflation gives weak bracing; over-inflation risks bursting.
Can in-box air bags secure a container load?
No. PE/LLDPE in-box bags only cushion small voids inside cartons; they carry no AAR rating and are not for container bracing.
Contact ICD Viet Nam
For the right dunnage bag for your load and void size, contact our team for specifications and 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
