The seal looked strong on paper. The burst testing results showed impressive numbers, well above the minimum threshold your customer specified. Quality signed off. Production continued. Then customer complaints started appearing, not about packages bursting open, but about products spoiling before their expiration date. The seals were strong enough to resist pressure. They just weren’t tight enough to keep air out.
This scenario plays out more often than packaging engineers like to admit. Burst test packaging provides valuable data about seal strength, but it answers a different question than many QA teams realize. Understanding what burst testing actually measures, and what it doesn’t, helps you build a testing program that catches the defects most likely to cause problems in the field.
What Is Burst Testing?
Burst testing is a destructive testing method that measures the internal pressure required to rupture a flexible package seal. The test pressurizes a sealed package with air until the seal fails, recording the pressure at the moment of failure. That pressure value, typically measured in pounds per square inch or kilopascals, indicates the mechanical strength of the seal.
Two primary ASTM standards govern burst testing for flexible packaging. ASTM F1140 covers unrestrained burst testing, where the package inflates freely during pressurization. ASTM F2054 covers restrained burst testing, where the package is held between rigid plates during pressurization to better control package expansion and distribute stress more evenly across the seal perimeter.
The distinction matters. When a package inflates freely under pressure, stress is strongly influenced by package geometry and film stretch. This means unrestrained testing may not consistently stress all seal areas equally. Restrained testing reduces ballooning and produces more seal-focused and repeatable stress conditions, improving the likelihood that seal weaknesses will be challenged during the test.
What is a burst test?
A burst test inflates a sealed package with air until the package ruptures. The test measures the maximum pressure the package withstands before failure occurs, providing a quantitative indicator of seal strength. The result tells you how much internal pressure your seals can handle before they give way.
Burst testing appears frequently in packaging validation protocols, particularly for medical devices and pharmaceutical products where regulatory bodies require documented evidence of seal strength. It’s also common in food packaging operations that need to verify their sealing process produces consistent results shift after shift.
How Burst Testing Works Step by Step
Step 1: Prepare the test specimen.
For most burst tests, the package is connected to a pressurization fixture or probe that allows controlled air introduction while maintaining an airtight seal. Specimens are often conditioned at standard temperature and humidity before testing if the environment is not already controlled.
Step 2: Mount the package in the test apparatus.
For unrestrained testing per ASTM F1140, the package inflates freely. For restrained testing per ASTM F2054, the package is placed between rigid plates to limit uncontrolled expansion and better focus stress on the seals.
Step 3: Apply pressure at a controlled rate.
Air is introduced at a controlled, documented rate defined in your SOP or validation protocol. Consistent ramp rates are critical to generating repeatable and meaningful data.
Step 4: Record the burst pressure.
Pressurization continues until the package ruptures. The equipment records the maximum pressure achieved before failure.
Step 5: Inspect the failure location.
If rupture occurs in the seal, the result reflects seal strength. If it occurs in the film, the material failed before the seal, which changes how the data should be interpreted.
Step 6: Document and analyze results.
Burst pressure, failure location, and test conditions are recorded and trended to assess process consistency and capability.
What Burst Testing Tells You About Seal Strength
Burst testing answers one question extremely well: how much internal pressure can this seal withstand before it ruptures?
It supports:
- sealing process validation
- incoming material qualification
- customer or regulatory strength requirements
- baseline performance benchmarking
- statistical process control and drift detection
Trending burst values over time often reveals equipment wear, temperature drift, or material variation long before catastrophic failures occur.
The Limits of Burst Testing for Daily QC
Strong seals and tight seals are not the same thing.
A seal can pass burst testing and still leak. Micro-channels, contamination, or incomplete fusion may not significantly weaken burst resistance but can allow oxygen, moisture, or microbes to pass at normal conditions.
Burst testing measures strength.
Leak testing measures integrity.
Burst testing is also destructive. Every tested unit becomes scrap. That limits sample sizes and makes it impractical as a high-frequency production QC tool.
Geometry also influences results. Burst testing finds the point that fails first, but it does not assess seal uniformity around the entire perimeter.
Does burst testing detect leaks?
No. Burst testing does not determine whether a seal is airtight. A package can pass burst testing and still leak. Leak detection requires integrity test methods such as bubble emission or vacuum decay.
Burst Test vs Bubble Emission: Choosing the Right Method
| Factor | Burst Testing (ASTM F1140/F2054) | Bubble Emission (ASTM D3078) |
| What it measures | Seal strength | Presence and location of leak paths |
| Test nature | Destructive | Does not rupture the package, though tested product is typically not released |
| Result type | Quantitative | Qualitative visual confirmation |
| Leak detection | No | Yes — gross and channel leaks (often cited around ~250 microns, depending on setup) |
| Shows defect location | Only after rupture | Yes, bubbles appear at leak sites |
| Best for | Validation, strength verification | Production QC, defect finding |
Burst testing belongs in validation and process qualification.
Bubble emission belongs in daily QC when the goal is to confirm packages do not leak.
Many strong QC programs use both.
When to Use Each Test in Your QC Program
Use burst testing when validating sealing processes, qualifying new materials, changing equipment or parameters, or satisfying customer and regulatory strength documentation requirements.
Use bubble emission testing when verifying packages are leak-free before shipping, identifying defect locations, investigating complaints, and performing frequent in-process checks.
Use both when regulatory validation and ongoing integrity monitoring are both required.
The worst approach is relying on burst testing alone and assuming strong seals mean leak-free packages.
Final takeaway
Burst test packaging measures something real and important — but not everything you need to know.
Seal strength matters.
Seal integrity protects your product.
For daily verification that packages will not leak before they reach customers, bubble emission testing per ASTM D3078 provides fast, visual confirmation without forced rupture.
FlexPak equipment brings both capabilities to your production floor. Validate strength when required. Verify integrity before product ships.