Prevent tears and leaks by matching the package film to the product and its filling, storage, and distribution conditions; keeping seal areas clean and flat; and validating the finished package with tests suited to the likely failure. First locate the defect: a split in the film body and a leak through a seal usually have different causes and call for different fixes.
Identify where the package is failing
Start with the failure location rather than changing sealer settings at random. A visible puncture or split through the film points toward film damage, handling stress, or a material that does not suit the application. A leak along a seal points toward an interruption in the seal or a process and geometry issue.
- Film-body damage: Look for cuts, fractures, punctures, or pinholes. Consider contact with equipment or other packages, stresses during filling and transport, and whether the film remains suitable at the storage temperature.
- Seal failure: Look for a channel, a section that did not bond, or an unsealed area. Product or other contamination, wrinkles, and creases can interrupt bonding or form a leak path.
The FDA inspection guide identifies cuts, fractures, channel leaks, and non-bonding as distinct defects; it also describes drop and peel testing in its inspection context: FDA Guide to Inspections of Low Acid Canned Food Manufacturers: Part 3.
Check the seal surface and package geometry
Remove contamination and wrinkles
Before sealing, keep the intended seal area free of product residue and other contaminants. Check that the film is not folded, creased, or wrinkled across the seal. These conditions are plausible causes of interrupted bonding, but inspecting them alone does not establish the root cause.
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Inspect corners, folds, and seal types
A seal does not experience identical conditions along its entire length. Corners, gussets, lap seals, and fin seals change the folded geometry and can have different local pressure and temperature requirements. A bag that seals well across a flat section may still have a weak region at a corner or fold. A 2023 study examined pressure and temperature effects in critical seal regions across the bag designs it tested; its findings are specific to those designs and conditions, not universal machine settings: Observing the effect of pressure and temperature on the seal integrity of critical seal regions of various flexible bag designs.
Match the film to the product and its route
Packaging material needs to suit the product, filling process, end use, and distribution conditions. Review whether the film can withstand the stresses imposed during filling, storage, and transport, and whether it is prone to pinholing in the relevant processing and handling conditions. For packages handled or stored cold, low-temperature flexibility matters as well.
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For medical primary flexible packaging, ASTM F2097 provides a framework for selecting applicable material, process, performance, and integrity evaluations. It does not set acceptance criteria for every package; selected methods must fit the product and purpose, and finished packages should be assessed under conditions of use. ASTM’s catalog presents F2097-25 as the active edition, while the cited guide is F2097-20. For technical work, check the current edition and its scope: ASTM F2097, Standard Guide for Design and Evaluation of Primary Flexible Packaging for Medical Products.
General packaging guidance also emphasizes film and foil strength, durability, and flexibility at low temperatures: FAO packaging guidance on film and foil.
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Set sealing conditions for the actual package
There is no single heat-sealer temperature, pressure, or dwell time that can be recommended for every flexible package. Seal performance depends on the material, equipment, contamination, process conditions, and package geometry. Establish settings for the particular film structure, thickness, sealer, and package design, then validate the result on representative filled packages.
Published figures illustrate why context matters. A 2021 review reports a minimum sealing pressure of 1.8 N/mm² and crease depths up to 150 μm in cited studies of lidding films and wrinkle or crease sealing. Those are study-specific observations, not general operating settings or acceptance criteria: Understanding the factors affecting the seal integrity in heat sealed flexible food packages: A review.
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Choose a test that can detect the failure you care about
Testing should match both the suspected defect and the protection the package must provide. ASTM lists seal-strength testing, visual seal inspection, and bubble-emission leak testing among relevant methods. The appropriate method and acceptance criteria depend on the package and intended product protection: ASTM Packaging Test Methods.
Bubble-emission testing: useful for gross leaks, not proof of no small leaks
ASTM D3078-02(2013) describes bubble-emission detection of gross leaks in flexible packages that contain headspace gas. Its catalog gives a sensitivity of 1 × 10⁻⁵ atm cm³/s or less sensitive in the cited interlaboratory context, and warns that small leaks may not be detected. Treat that figure as a description of the method, not a universal package-acceptance threshold. Results depend on the product, packaging material, and test parameters: ASTM D3078, Standard Test Method for Determination of Leaks in Flexible Packaging by Bubble Emission.
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Use complementary checks where appropriate
Visual inspection can reveal visible discontinuities; seal-strength or peel tests can assess bonding; and drop testing can help evaluate package behavior under an impact challenge. These checks answer different questions, so a passing result from one method does not automatically establish performance in every use condition. For sterile pharmaceutical products, USP General Chapter 1207 addresses package-integrity evaluation within that specific scope: USP General Chapter 1207, Package Integrity Evaluation—Sterile Products.
Quick Recap
A practical troubleshooting sequence
- Locate the defect. Record whether the failure is through the film, along a seal, or at a fold, corner, or closure. Distinguish a puncture or fracture from a channel or unbonded section.
- Inspect the affected region. Check for product residue, other contamination, wrinkles, creases, folds, and damage from handling. Pay particular attention to corners, gussets, and fin or lap seals.
- Review the application. Confirm the film is suitable for the packed product, filling process, storage temperature, and expected distribution stresses. Consider low-temperature flexibility and pinholing when those conditions apply.
- Adjust the specific process, not a generic setting. For a seal failure, review the material, equipment conditions, and package geometry together. Establish settings for that combination rather than applying a universal temperature or pressure.
- Validate the change on representative packages. Test finished packages in conditions that reflect their intended use, selecting integrity, seal-quality, and distribution checks for the failure mode. Do not treat a gross-leak test as evidence that every small leak is absent.
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