A dunnage bag only protects cargo when it is inflated correctly. Under-inflate it and the load can shift; over-inflate it and the bag itself can burst. The good news: the whole job takes a few minutes per bag, and the steps below work for both paper (kraft) and poly-woven (PP) dunnage bags.

1. Measure the Gap First, Then Choose the Bag

Before you pick up a bag, measure the void between the cargo units or between cargo and the container wall. Dunnage bags are sized to a gap range — a bag that is too small for the gap will never fill it firmly, and a bag that is far too large will fold, crease, and take pressure unevenly. As a rule, choose a bag whose rated gap range covers your measured void, and check the manufacturer's size chart rather than guessing from the bag's flat dimensions. For reference, Tezheng's published range covers gaps of 10–50 cm across six bag sizes.

If the gap varies along the load — wide at the top, narrow at the bottom, for example — measure at the widest point and place the bag where it can bear evenly. An uneven gap is also a sign to check whether the load itself needs re-stacking before you bag it.

2. Position the Bag Flat, Centered, Valve Out

Unfold the bag fully and slide it into the gap so that it sits flat, centered, and uncreased. The valve should face outward, where the inflation gun can reach it easily and where you can check it later. Keep the bag away from sharp edges: container wall burrs, protruding nails, and sharp carton corners are the most common causes of punctures. If you spot a burr or a sharp corner, cover it with cardboard before the bag goes in — a minute of preparation prevents a burst bag mid-voyage.

Never twist or fold a bag to make it fit a gap it was not sized for. A folded bag inflates unevenly, and the folded edge becomes a weak point.

3. Inflate Slowly, and Watch the Bag — Not Just the Gauge

Connect the inflation gun or hose to the valve and inflate slowly and evenly. Watch three things as the bag fills:

• Fullness: the bag should fill the gap completely, pressing firmly against both cargo faces without bulging sideways out of the gap.
• Feel: press the bag surface — it should feel firm and springy, like a well-inflated ball, not rock-hard and not soft.
• Load movement: try to rock the cargo gently. If it no longer shifts, the bag is doing its job.

On pressure: there is no single universal number. Never exceed the manufacturer's rated maximum pressure for the bag you are using; a commonly referenced ceiling for standard bags is 0.3 bar, but the rating on your specific bag and the gap width are what actually decide the right pressure. Inflate to "full, firm, and holding the load still" and stop there — more pressure is not more protection, it is more burst risk. For the full reasoning, see our guide on dunnage bag inflation pressure standards.

4. Wait a Few Minutes, Then Re-Check

After inflation, wait a few minutes and check again. A bag that slowly softens in those first minutes has a leak — usually at the valve or a small puncture — and should be replaced now, not discovered at destination. Also re-check the load: cargo settles slightly as the bag presses in, and a quick second look catches a bag that needs a small top-up. This re-check takes under a minute per bag and is the cheapest insurance in the whole loading process.

5. Common Mistakes to Avoid

• Over-inflation: the number one cause of burst bags. If the bag feels rock-hard, let some air out.
• Wrong size for the gap: a bag stretched across too wide a gap works at its limit from the first minute.
• Inflating against sharp edges: check the gap for burrs and corners first, every time.
• Skipping the re-check: a slow leak found at loading costs one bag; found at destination, it can cost a damaged load.
• Reusing a patched bag: a bag that has been patched is an emergency measure, not a loading standard — use a new bag for the next shipment.

For the other side of this topic — what to do when a bag fails in transit — see how to use a dunnage bag in a container, and for storage between shipments, how to store dunnage bags before use.

Frequently Asked Questions

How do you inflate a dunnage bag?

Measure the gap, choose a bag sized for that gap, position it flat and centered with the valve facing out, then inflate slowly with a gun or hose until the bag is full, firm and springy, and the cargo no longer shifts. Never exceed the manufacturer's rated maximum pressure, and re-check the bag after a few minutes for slow leaks.

What pressure should a dunnage bag be inflated to?

There is no single universal pressure: it depends on the bag's rated maximum and the gap width. A commonly referenced ceiling for standard bags is 0.3 bar, but always follow the rating printed for your specific bag, and judge by fullness and firmness — full, firm, springy, and holding the load still — rather than chasing a number.

Can you inflate a dunnage bag with a regular air compressor?

Yes, provided you use a compatible inflation gun or nozzle with a controllable flow, and you inflate slowly. A high-pressure, uncontrolled air line is risky: it can overshoot the rated pressure in seconds. Use a gun with a trigger you can feather, and stop as soon as the bag is firm.

How do you know when a dunnage bag is full enough?

Three checks: the bag fills the gap completely without bulging out sideways; pressing it feels firm and springy, not rock-hard or soft; and the cargo no longer rocks when pushed gently. If any of the three fails, adjust — top up, let air out, or reposition the bag.

Can a dunnage bag be re-inflated during transit?

If the container is opened mid-route and a bag has softened, it can be topped up — but only if the bag itself is undamaged. A bag that softened because of a puncture or a torn valve should be replaced, not re-inflated, since it will leak again.

Related reading: Dunnage Bag — product page and How to Store Dunnage Bags Before Use. Ordering note: Tezheng's export MOQ for dunnage bags is 5,000 pieces, with a lead time of about 20 days from production to port; our dunnage bags carry an SGS report covering chemical safety (TPCH toxics in packaging), not a railroad performance certification.