One leaking bag can cost you a whole shipment. For liquid products — fertilizer, juice, syrup, dairy — a burst bag in transit doesn't just mean lost product. It means contaminated pallets, rejected deliveries, and a customer who won't reorder.

 

After 24 years of manufacturing flexible liquid packaging, we've identified four factors that determine whether a bag holds up or breaks down. Here's what to look for.

 

1. Delamination Strength: Are Your Layers Working Together?

A composite film bag is only as strong as the bond between its layers. If the adhesive fails — what we call delamination — the layers separate under stress, and the bag tears at its weakest point.

This is especially common in high-temperature applications. Some adhesives lose grip at 121°C, causing seal-edge delamination and leakage in retort pouches. In frozen environments, poor interlayer bonding leads to brittle cracks.

What to check: Ask your supplier for peel strength test data. At Qichen, every batch is tested on our electronic tensile tester (GLB-L2) — peel strength must exceed 4N/15mm before a bag leaves our facility.

 

2. The Bag-Making Process: Heat, Pressure, and Precision

A well-designed film can still fail if the bag is badly made. Three common problems:

l  Temperature too high: Overheating degrades the heat-seal layer, weakening the seal. This bag passes visual inspection but fails under load — what we call a "cold seal" that's actually been burned.

l  Pressure too high: Excessive sealing pressure squeezes out the sealant material, leaving a thin, fragile seam.

l  Cutting edge too sharp: A blade that's too sharp or misaligned will nick the heat-seal edge, creating a micro-tear that propagates under stress.

What to check: The heat seal should be ≥6mm wide and uniform across the entire seal line. At Qichen, our heat-seal strength guarantee is ≥40 N/15mm — tested in both machine direction and transverse direction.

 

3. Material Selection: Getting the Formula Right

Several material factors directly affect breakage resistance:

l  Thickness matters. A film that's too thin won't have enough tensile strength, period. But thickness alone isn't enough — what's inside the film matters more.

l  Vigilant about recycled content. Some manufacturers blend recycled material (regrind) into the PE layer to cut costs. Regrind reduces strength across every metric — tensile, elongation, impact, seal. A bag with 20% regrind might pass visual QC but fail a 1-meter drop.

l  Add LLDPE or mPE for toughness. Adding linear low-density PE (LLDPE) or metallocene PE (mPE) to the inner layer dramatically improves impact strength and flexibility, reducing breakage without adding thickness.

l  Cold environments need cold-rated films. Standard PE turns brittle below freezing. For products shipped or stored in cold conditions, the film must be formulated with cold-resistant components like BOPA (nylon).

At Qichen, our standard oil-bag structure (PA/PE + PE, 55μm + 50μm) achieves a tensile strength that handles 1500N of compressive force for 1 hour — with zero leakage.

 

4. Real Application Testing: The Lab vs. The Truck

The best way to predict breakage? Test like reality, not like a lab.

At Qichen, every new bag structure goes through:

l  Drop test (LH-1500 Single-Arm Drop Tester): 1-meter free-fall drop onto concrete, filled with actual product at operating weight. Pass = no leakage, no seal damage. This is the single most predictive test — if a bag survives a 1-meter drop, it survives logistics.

l  Compression test: 1500N sustained for 1 hour. Simulates the bottom bag in a stacked pallet on a bumpy road.

l  Friction coefficient (Coefficient of Friction Tester): Ensures bags feed smoothly through automated filling lines without jamming or tearing. 

Microbial incubation (303-0B Electric Incubator): For aseptic bags, we incubate filled samples to verify sterility holds over time.

We also offer on-site testing support — if your filling line is in Lanzhou or Xinjiang, we'll send samples and walk through the testing process with your team.

A bag that leaks isn't just a packaging failure — it's a business failure. The difference between a bag that holds and a bag that bursts often comes down to one of these four factors. Before your next order, ask your supplier: what's your peel strength? What's your heat-seal guarantee? Do you drop-test every new structure?

If they can't answer, we can.

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Qichen Packaging (Wuxi) Co., Ltd | www.qcpackage.com | info@qcpackage.com

24 years of liquid flexible packaging. Standardized tested before delivery.