Last updated: March 2026
A bag of chips makes it through the sealer. It holds on the line. It holds through the warehouse. Then it blows out on a pallet somewhere between your plant and the retailer — because the seal was right at its limit, and nobody knew.
Burst testing is how you find that limit before your customer does. But it’s one piece of a complete QA program, not the whole picture. This guide explains what burst testing actually measures under ASTM F1140, when it’s the right test to run, and where it needs to be paired with leak detection to give you full confidence in your packaging.
What Does Burst Testing Actually Measure?
Burst testing measures the maximum internal pressure a sealed package can withstand before the seal fails. A package is pressurized from the inside — either by inflating it or compressing it from the outside — until the seal gives way. The pressure at failure is your burst strength.
That number tells you something specific and useful: whether your sealing process is producing seals that meet specification. It’s a process control tool. If burst strength starts dropping across a production run, something has changed — seal bar temperature, dwell time, material lot, or line pressure. Burst testing catches that drift.
What it doesn’t tell you is whether the finished package is leak-free. A package can pass burst testing with strong, consistent numbers and still have a channel defect or pinhole that allows oxygen ingress over time. Seal strength and seal integrity are different measurements. A complete QA program needs both.
ASTM F1140: The Standard Behind Burst Testing
The governing standard for burst testing of flexible packaging is ASTM F1140. It covers two test methods:
Method A — Restrained Burst: The package is placed between two plates and pressurized from the inside. The plates restrain the package from expanding, so the test isolates seal strength directly. This is the most common method for flexible pouches and bags.
Method B — Unrestrained Burst: The package is pressurized without restraint, allowing it to expand freely until failure. This method is used when you want to simulate real-world pressure conditions more closely, or when the package geometry doesn’t lend itself to plate restraint.
Both methods produce a burst pressure value — the point at which the weakest seal fails. ASTM F1140 requires establishing a test pressure based on a control sample containing a known defect, and results are reported as pass/fail at a defined threshold, not as a continuous leak rate measurement.
A companion standard, ASTM F2054, covers burst testing specifically for medical packages — relevant for pharmaceutical food supplement and medical nutrition applications where ISO 11607 compliance is a consideration.
Burst Testing vs. Leak Integrity Testing: Why You Need Both
This is where most QA programs have a gap. Burst testing and leak integrity testing are often treated as interchangeable. They’re not.
| Factor | Burst Testing (ASTM F1140) | Bubble Emission Testing (ASTM D3078) |
|---|---|---|
| What it measures | Maximum seal strength before failure | Whether a finished package is leak-free |
| Test type | Destructive | Non-destructive |
| What it catches | Weak or inconsistent seals | Channel defects, pinholes, seal failures |
| Result format | Burst pressure value (pass/fail) | Visual bubble stream at failure location |
| Best use | Process control and seal consistency | Package integrity verification |
| Headspace required? | No | Yes (or VAC Attachment for vacuum-sealed packs) |
| Production use | Sample testing | Can be run on every unit |
The practical implication: burst testing confirms your sealing process is in spec. Bubble emission testing under ASTM D3078 confirms the finished package will actually hold up through distribution, storage, and shelf life.
A seal can be mechanically strong — passing burst testing at full specification — and still have a channel defect that allows oxygen ingress. That defect won’t show up on a burst test. It will show up as stale product, a shortened shelf life, or a customer complaint three weeks after the package shipped.
The programs that prevent recalls run both.
Which Packaging Formats Is Burst Testing Right For?
Burst testing under ASTM F1140 is most appropriate for:
Flexible pouches with heat-seal closures — stand-up pouches, flat pouches, pillow packs. The restrained burst method (Method A) works well for these formats. Burst testing is a standard part of seal validation for snack food, pet food, coffee, and dry goods applications.
Flow-wrap and form-fill-seal packaging — horizontal and vertical FFS formats where consistent seal bar performance is critical to maintaining burst strength across a production run.
Retort and high-pressure processed pouches — where the packaging must survive both the processing environment and subsequent distribution without seal failure. Burst testing is part of the qualification protocol for these formats.
Medical nutrition and pharmaceutical food supplement packaging — where burst testing under ASTM F1140 or F2054 is used alongside bubble emission testing (ASTM F2096 via the FPIPA attachment) to satisfy both strength and integrity requirements.
For rigid containers with threaded or lug closures — condiment bottles, jars, sachets with rigid closures — burst testing under F1140 is not the right method. ASTM D5094 (dry chamber testing) is the appropriate gross leak test for closure integrity on rigid food containers. See the dry chamber testing guide for more on that format.
How to Build Burst Testing Into Your QA Cadence
Burst testing is most valuable as a process control tool run consistently — not as an occasional audit. Here’s how a practical QA cadence looks for packaging lines running burst testing alongside integrity testing:
Start of shift: Run a burst test on samples before production begins. This confirms your seal bar is at temperature, dwell time is set correctly, and your sealing parameters haven’t drifted overnight. If burst strength is below spec at the start of shift, you haven’t compromised a production run — you’ve caught the problem before it starts.
Periodic spot checks: At minimum, one burst test per hour during production. This is your real-time signal for seal quality drift. A gradual drop in burst strength across a shift is one of the most common precursors to in-field failures — and it’s nearly invisible without consistent testing.
Material changeovers: Any time you swap film lots, adjust seal bar settings, or change seal bar temperature or dwell time — test immediately before continuing production. Material lot variation is a significant source of burst strength variation that doesn’t show up until something fails downstream.
End of shift: Pull one final sample. Seal quality that degrades gradually across a run is common and often goes undetected without a closing test.
Pair with integrity testing: Burst testing tells you whether your seals are strong. Bubble emission testing under ASTM D3078 tells you whether they’re leak-free. Running both on the same cadence gives you a complete picture — process control plus package verification.
For manufacturers following ISO 2859-1 sampling frameworks, seal strength testing typically falls under the critical defect category. The specifics depend on your product risk level and customer requirements. A practical rule: review your testing frequency after three to six months of data. Consistent results may allow you to adjust frequency. Inconsistent results are a signal to increase it.
FlexPak Equipment for Burst and Integrity Testing
FlexPak package leak detectors are designed for food manufacturing QA environments — fast results, simple operation, and ASTM-compliant testing.
For complete flexible packaging QA, the core FlexPak unit runs ASTM D3078 bubble emission testing and ASTM D6653 altitude simulation. The FPIPA attachment adds ASTM F2096 internal pressurization capability for tray and pouch formats. The VAC Attachment makes vacuum-sealed packages testable under D3078 without damaging the product.
Results in around 30 seconds. Visual confirmation of the exact leak location — not just a pass/fail signal.
See which FlexPak unit fits your packaging format →
For a deeper look at related test methods:
- How to perform a bubble leak test (ASTM D3078) →
- ASTM F2096 practical guide →
- ASTM D6653 altitude simulation guide →
- Seal strength vs. seal integrity testing →
- Choosing the right leak tester for your packaging →
- Food packaging testing methods overview →
Frequently Asked Questions
What is burst testing in packaging?
Burst testing measures the maximum internal pressure a sealed package can withstand before its seal fails. It’s used as a process control tool to confirm that your sealing equipment is producing seals that meet specification — and to catch seal strength drift before it results in failures in distribution.
What ASTM standard governs burst testing?
ASTM F1140 is the primary standard for burst testing of flexible packaging. It covers two methods: Method A (restrained burst, where plates prevent the package from expanding) and Method B (unrestrained burst, where the package expands freely under pressure). ASTM F2054 covers burst testing for medical packaging applications.
Is burst testing the same as leak testing?
No — and this distinction matters. Burst testing measures seal strength: the pressure required to make a seal fail. Leak testing evaluates whether a finished package is actually leak-free under real-world conditions. A package can pass burst testing and still have a channel defect or pinhole that allows oxygen ingress. A complete QA program uses both.
What packaging formats is burst testing used for?
Burst testing under ASTM F1140 is most commonly used for flexible pouches, flow-wrap, form-fill-seal packaging, retort pouches, and medical nutrition packaging. For rigid containers with threaded or lug closures, ASTM D5094 (dry chamber testing) is the appropriate method.
How often should I run burst tests during production?
At minimum: start of shift, once per hour during production, after any material changeover or machine adjustment, and end of shift. This cadence catches seal quality drift while there’s still time to correct the line. Pair burst testing with bubble emission testing under ASTM D3078 for a complete picture of both seal strength and package integrity.
Burst testing is a reliable process control tool — but it’s one part of a complete QA program, not the whole thing. If your current testing tells you whether seals are strong but not whether packages are actually leak-free, that’s the gap worth closing.
If you’re not sure which test methods fit your packaging format, FlexPak can help you find the right solution.