Ask a supplier "what is it made of" and you will usually get a one-word answer — paper, or woven. That answer hides the part that actually matters: a dunnage bag is not one material, it is a structure. The outer layer and the inner layer do different jobs, and they fail in different ways. Knowing which layer does what is how you choose the right bag, and how you judge whether a used bag is still safe.

How a dunnage bag is built: outer layer plus inner bladder

Every dunnage bag has the same two-part job. The inner bladder — a PE film — is the airtight layer: it holds the compressed air and keeps pressure through the trip. The outer layer is the structural layer: it resists the pressure from inside, protects the bladder from the cargo, and spreads the load across the bag's surface. When a bag bursts, it is usually the outer layer that has been cut, worn thin or over-stressed first, and the bladder then fails through that weak point. That is why two bags with the same inner film can behave very differently: the outer material changes everything.

Kraft paper composite bags: the standard single-trip bag

The kraft paper bag's outer is several layers of kraft paper laminated together, with the PE film inside. It is light, cost-effective and well suited to standard container loads on a single trip. Its limits are also clear: paper wears against cargo, weakens when damp, and — once used — its remaining strength is hard to judge by eye, because paper can lose strength without showing an obvious tear. That is why kraft paper bags are generally treated as single-use: not because they always fail on a second trip, but because a second trip's safety cannot be verified reliably. For the full reuse logic, see how to dispose of used dunnage bags and our sizing guide what size dunnage bag do I need.

PP woven bags: for rough, damp or repeated use

The PP woven bag replaces the paper outer with woven polypropylene fabric — the same family of material used in woven sacks and bulk bags — over a PE inner bladder. Woven fabric resists tearing and abrasion far better than paper, tolerates damp conditions better, and keeps a more predictable strength after use, which is why PP woven bags can be reused several times when inspected and found undamaged: no cuts, no seam failure, valve working, no moisture or oil contamination. For sharp-edged cargo, rough pallets or fixed routes where bags travel back and forth, PP woven is the safer material choice. It costs more per bag, but the cost per trip falls with each reuse.

Choosing between them: three questions

First, what is the cargo like? Smooth cartons on a single trip: kraft paper is fine. Sharp metal edges, rough timber, protruding nails: choose PP woven, and still protect sharp points with a board or pad — no bag material is meant to be pressed directly against a sharp point. Second, will the bag be reused? If yes, PP woven; if the route is one-way and the load is standard, kraft paper is the economical choice. Third, will it get wet? Damp holds, rain exposure during loading or condensation in the container all favour PP woven. When in doubt, send us the cargo type and void size — matching material to cargo is exactly what samples are for.

A note on certifications: SGS is chemical safety, not AAR

One point of confusion is worth stating plainly. Tezheng's SGS report covers chemical safety testing (TPCH). It is not a railway performance certification: the US railway system requires AAR certification, which is a separate standard with its own testing. An SGS chemical safety report should not be presented — by us or anyone else — as proof of AAR approval. If your cargo moves by US rail and the receiver asks for AAR, ask for the AAR document itself.

What material are dunnage bags made of?

Kraft paper composite bags (multi-layer kraft paper outer, PE film inner) or PP woven bags (polypropylene woven outer, PE inner bladder). The inner film holds the air; the outer layer carries the load.

Which is stronger, kraft paper or PP woven?

PP woven resists tearing, abrasion and moisture better, and can be reused when inspected and undamaged. Kraft paper is the economical standard for single trips with smooth cargo.

Are dunnage bags recyclable?

It depends on material and local rules: the PE inner film makes the bag a composite product, not plain paper. Deflate used bags and check local waste rules before disposal.

What is the MOQ and lead time?

Tezheng's export MOQ is 5,000 bags for dunnage bags, with a lead time of about 20 days from production to port. Order samples first and trial the material on a real load before placing a bulk order.

Related reading: what size dunnage bag do I need and how to inflate a dunnage bag.