Short answer: a weak seal is rarely explained by “bad film” alone. Start with the failure pattern, then check contamination, temperature, dwell time, pressure, jaw condition and the sealant layer. Change the material only after you know which part of the seal window is failing.
First, describe the failure—not the suspected cause
- Seal peels open cleanly: the seal may not have reached a workable temperature, dwell or pressure.
- Seal tears through one layer: the interface may be stronger than the adjacent material; compare this with the approved sample.
- Only some packs leak: look for tea dust, folds, jaw contamination, uneven pressure or intermittent registration.
- Seals pass at the factory but fail later: review cooling, pack handling, compression, temperature during shipping and product oils or aroma interaction.
Use this order of checks on the line
- Clean the seal area and jaws; remove tea dust or product contamination.
- Confirm the actual jaw temperature rather than relying only on the display.
- Record dwell time, pressure and line speed together.
- Check that the web tracks correctly and the seal area is not folded or stretched.
- Compare the sealant side and complete structure with the approved material.
- Repeat the test with a controlled sample and record the result.
Changing several settings at once hides the cause. Make one controlled adjustment at a time and keep failed and passed samples.
Material questions to send the supplier
Ask for the complete layer sequence, sealant type, total thickness, seal orientation and the sample or specification that was approved. A generic name such as “PET/PE” or “paper laminate” is not enough to predict the seal window. For tea outer wrappers, also state whether the line uses heat seal or cold seal and provide the repeat, width and winding direction.
When the packaging format changes the diagnosis
An individually wrapped tea bag uses a different route from a retail stand-up pouch. Use the Tea Bag Outer Wrapper page for wrapper rollstock. For a paper-led structure where sealing is the main issue, compare High-Seal Aluminum Paper Rollstock. A finished premade pouch needs its own zipper, gusset and pouch-making checks.
What to include in a corrective-action brief
Send an unused roll sample, failed packs, photos of the seal, complete structure, machine model, jaw style, speed, temperature, dwell, pressure, packed product, filling weight and when the failure appears. State the acceptance test you use—peel, leak, burst, drop or another agreed method.
Ask for a controlled seal review
Use the Tea RFQ to send the failed sample, line settings and structure. XLD will identify the missing information and whether the next step should be a setting review, material comparison or trial roll.
Last reviewed: 13 October 2026.
