Packaging quality control inspection and documentation — Packaging example from the Bowen New Material website.

Quick answer: Check flexible packaging with a combination of visual inspection, seal-strength testing, an appropriate leak test and filled-pack handling trials. Each checks a different failure mode. A strong seal can still contain a leak channel, and a leak-free sample does not prove that a whole production lot is acceptable.

Film selection is only one part of packaging performance. A folded corner, product dust in the seal, an unsuitable sealing setting or a damaged closure can undermine an otherwise suitable bag. This buyer’s guide explains how to turn a vague request for strong bags into an inspection plan that a supplier and buyer can both follow.

Seal strength vs seal integrity: what is the difference?

Seal strength describes resistance to separation. Seal integrity concerns continuity of the seal and whether unwanted leak paths are present. Treat them as separate requirements when approving pouches, zipper bags or vacuum bags.

Check	What it tells you	What it does not prove
Visual inspection	Whether visible wrinkles, contamination, missing seals or alignment defects exist	The absence of every small leak or sufficient mechanical strength.
Seal-strength test	How a defined seal specimen resists separation and how it fails	That the complete package has no leakage paths.
Suitable leak test	Whether the method detects leakage in the tested pack under stated conditions	Unlimited sensitivity, shelf life or full-lot conformity.
Filled-pack handling trial	Whether the actual pack survives the agreed handling scenario	Performance on every route or under untested conditions.

Start with a visual inspection of the finished pack

Look along the side seals, bottom corners and final top seal. Check for product trapped in the sealing zone, creases crossing the seal, burn-through, inconsistent seal width and damaged zipper tracks. For valve pouches, inspect the valve attachment separately. Photograph defects beside a scale and identify the production lot.

Define cosmetic and functional defects separately. A small print variation and an open channel through the seal should not have the same acceptance rule. Record which defects cause rejection, what can be reworked and how a retest is documented.

Use seal-strength results that can be compared

ASTM F88/F88M describes measuring the force needed to separate a specimen containing a seal and identifying its failure mode. When requesting results, specify the applicable method, specimen width, conditioning, test speed, specimen support and reporting units.

Do not compare a number reported in newtons with a value expressed per unit width until the specimen basis is understood. A film tear, delamination and separation at the seal interface also tell different stories. Require the failure description alongside the result.

Set acceptance limits for your material, product and use case with the supplier or testing laboratory. There is no single seal-strength threshold that makes every flexible pouch fit for purpose.

Choose a leak test for the package, not just a familiar name

A laboratory should select a method appropriate to the structure, contents, closure and required detection capability. ASTM lists F2096 as a gross-leak test using internal pressurization. A gross-leak result should not be interpreted as proof that every smaller leak is absent.

Document the preparation, pressure or vacuum conditions, observation time and pass/fail rule for the selected method. Valves and intentional openings need special consideration because they may release gas by design. An improvised squeeze test can help screen samples, but it is not a substitute for an agreed test protocol.

Validate the sealing process on your filling line

Ask for the recommended sealing window, then verify it with your equipment and actual product. Temperature, dwell time and pressure work together; jaw temperature alone does not describe the complete process. Check startup conditions as well as normal running speed, and challenge realistic contamination or handling variation within an agreed plan.

A resealable zipper is not automatically the primary protective seal. If the pack requires a separate heat seal above the zipper, inspect and test that seal after filling. For machine-specific considerations, see our vacuum packaging bag guide.

Build a lot acceptance record

Approved bag drawing, material structure and specification revision.
Production lot, sampling locations, sample count and agreed sampling plan.
Visual defect definitions and functional rejection rules.
Test method, equipment identification, conditions and acceptance limits.
Measured results, failure modes, photographs and any retest decisions.
Retained samples and traceability to the delivered cartons.

Do not invent a sampling plan after discovering a defect. Agree the plan before production, including how a failed sample affects lot disposition. Pre-shipment inspection is one stage; incoming checks and filled-pack trials still have a role.

Keep barrier performance separate from sealing performance

OTR and WVTR describe transmission through material under stated test conditions. ASTM describes oxygen transmission in D3985 and water-vapor transmission in F1249. Film data alone cannot confirm the complete filled package’s shelf life.

Use the barrier properties guide for material comparisons. Confirm capacity with the stand-up pouch sizing guide and include the inspection requirements in your packaging RFQ checklist. Food-contact documentation should be reviewed separately for the intended product and market.

Bowen New Material (Dongguan) Co., Ltd. supplies custom flexible packaging. Send your product, filling process and inspection requirements to discuss a suitable bag specification and which tests need to be agreed before ordering.

Frequently asked questions

Does a strong seal mean a pouch is leak-free?

No. A mechanically strong seal may contain a channel or local defect. Check strength and integrity with appropriate, separate methods.

Is a zipper enough to protect an unopened food pouch?

That depends on the package design. Many resealable pouches also need a final heat seal above the zipper. Validate the complete closed pack for its intended use.

What seal-strength number should I request?

Request a result with the test method, specimen width, units, conditions and failure mode. Agree a product-specific acceptance limit rather than copying an unrelated value.

Can a leak test establish shelf life?

No. Shelf life also depends on the product, barrier structure, storage, distribution and filling conditions. A leak test checks only the failure modes covered by its method.