Stand-Up Pouch Seals Leaking or Peeling After Filling: How to Find and Fix the Cause

First question: who made the seal that failed?

A pre-made stand-up pouch has two kinds of seals. The side seals, bottom gusset and zipper seals are made by the pouch converter. The top seal is usually made by the brand or co-packer after filling, on their own heat sealer. Knowing which seal failed tells you where to look and who needs to change something. Mark each leaking pouch at the exact leak point before you start testing, and keep a few unopened failed pouches for the supplier.

Read the failed seal

Pull a failed seal apart slowly and look at it. If the two inner layers separate cleanly and look almost unsealed, the seal was likely too cold, too short or contaminated. If the seal edge looks thin, glossy or distorted, the film may have been overheated so that the sealant squeezed out and weakened the edge. If the outer printed layer separates from the inner layers instead, that is delamination of the laminate rather than a seal failure, and it is a material or curing question for the converter. If the film tears beside an intact seal, the seal is stronger than the film and the problem is more likely handling, drop or overfill stress.

Common causes and fixes

1. Contamination in the seal area. Fine powders, oily products and splashing liquids are the most frequent cause of top-seal leaks. Use a funnel or nozzle that reaches into the pouch, keep the seal zone clean, allow dust to settle before sealing, and ask the converter whether a sealant layer that tolerates contamination better is available.
2. Settings outside the seal window. Every film has a range of temperature, dwell time and pressure that makes a good seal. Too low gives weak seals; too high can thin and weaken the seal edge. Ask the supplier for the recommended sealing range for your film and confirm it with a short ladder test on your own sealer.
3. Narrow windows on recyclable and compostable films. Mono-material and compostable structures often seal within a narrower range and may have less heat resistance than traditional laminates, so settings that worked for an older pouch may not transfer. Re-validate when you change material; the mono-PE versus foil comparison explains the trade-offs.
4. Overfilling and headspace. Product pressing on the seal, or a fill level too close to the seal line, both cause leaks and peeling under load. Check that the pouch size fits the fill weight and leaves room above the product.
5. Impulse sealer technique. Small brands often use impulse or hand sealers. Hold pressure through the cooling phase, keep the heating band and cover clean, and check that the seal width is not narrower than the pouch design expects.
6. Gusset corners. If leaks cluster at the bottom corners across many pouches, share the evidence with the converter. Bottom seal settings, gusset folding and corner design are their process, not the filler's.
7. Pressure changes in transit. Air freight and mountain routes reduce outside pressure, so sealed pouches with trapped air can balloon and stress the seals. Reduce excess air where the product allows.

Tests to run on filled pouches

• Squeeze test: press the filled, sealed pouch gently and listen and feel for air escaping. Quick and useful for sorting.
• Water inversion test: for liquid or wet products, fill a few pouches with water, seal, lay them on paper towels upside down and check for damp spots after a set time.
• Bubble test: submerge sealed pouches with some air inside, apply light pressure or vacuum, and watch where bubbles appear. ASTM D3078 is a recognised bubble-emission leak method.
• Seal strength (peel) test: cut strips across the seal and pull them apart on a tensile tester. ASTM F88 is the common reference method; compare results between settings rather than against a figure from another product.
• Drop test: drop filled pouches from a realistic height onto the bottom and the side, then repeat the squeeze test.

Typical acceptance values depend on the film, pouch size and product. Agree the method and pass level on approved samples rather than copying a number from elsewhere.

What to send the supplier

• Product type (powder, granule, liquid, oily or sharp) and fill weight
• Filling method and the make and type of your sealer, including jaw width
• Pouch size, film structure, zipper type and position, and the stand-up pouch dieline used
• Photos with leak points marked, lot numbers and how many pouches were affected
• Storage and shipping conditions, including air freight or refrigeration

Common mistakes

• Testing seal settings on empty pouches when product dust is the real problem.
• Switching to a recyclable or compostable film without re-checking sealer settings.
• Filling to the brim because the pouch looks too large on the shelf.
• Judging seals by appearance only; a seal can look good and still leak at a corner.
• Assuming the zipper makes the pouch airtight before the top seal is opened.

Related pages

• Custom stand-up pouches
• Custom flat bottom pouches
• Pouch zipper types compared
• Contact BestPackFactory