Quality assurance doesn’t leave room for guesswork, especially in food, pharmaceutical, and medical packaging. In 2023 alone, over 30 product recalls in the U.S. cited “packaging failure” or “seal integrity issues.” One of the most trusted frontline tools against these failures? Bubble emission testing.
But the difference between passing an audit and shipping a liability often comes down to how well that test is performed. This guide explains how ASTM D3078 bubble testing works under pressure. We’ll walk through proper technique, highlight common missteps, and give QA leads the tools they need to make decisions they can stand behind during any inspection.
What Is Bubble Testing for Flexible Packaging?
Bubble emission testing, or “bubble testing,” refers to a method of leak detection defined under ASTM D3078. It’s designed specifically for flexible packaging with internal headspace, typically pouches or trays filled with air or modified atmosphere gas.
During the test, the package is submerged in water inside a vacuum chamber. As the pressure drops, any leaks in the seal or film will force air/gas to escape—forming visible bubbles. If no bubbles appear, the package passes. If a steady stream is observed, the seal has failed.
But not all bubble testing is equal. ASTM D3078 sets clear parameters for vacuum level, hold time, and equipment setup—yet leaves certain values flexible so manufacturers can adapt the method to different product lines. This flexibility is helpful—but it also introduces risk when teams guess instead of test.
Core components of an ASTM D3078 setup include:
- Transparent vacuum chamber with a tight-sealing lid
- Vacuum gauge and inlet/outlet valves
- Submersion fluid that doesn’t degrade the package (i.e. water)
- Conditioning protocol to bring fluid and package to room temperature
- Controlled vacuum pull (slow enough to avoid rupture)
If done correctly, the test can detect gross leaks ≥1×10⁻⁵ atm cm³/s. That’s roughly 1/10 the thickness of a human hair, but still plenty large enough to compromise sterility, shelf life, or safety of a product.
But for QA leads, understanding when it’s the right test—not just how to perform it—is equally important.
When Should You Use ASTM D3078 Bubble Testing?
Not all flexible packages are good candidates for bubble testing. ASTM D3078 relies on the presence of headspace air or gas to create pressure differentials during vacuum application. Without it, there’s nothing to expand—and no bubbles to form, even if the seal is faulty.
Use ASTM D3078 when:
- The package has ample headspace (air or MAP)
- You’re checking for gross leaks, not micro-leaks (yes, 1/10 the thickness of a human hair is still a gross leak!)
- The seal is strong enough to tolerate vacuum exposure
- The contents won’t mask or clog a potential leak
For example, a snack pouch with a nitrogen flush is an ideal candidate. A vacuum-sealed medical device pouch with no headspace is not.
If you test the wrong package with this method, you might walk away with a false negative—thinking the seal is good when it’s quietly failing. This is where ASTM F2096 comes in. It uses internal pressurization to detect leaks in vacuum-sealed or non-headspace packaging.
| Package Type | Best Test Method | Why |
| Air-filled flexible bag | ASTM D3078 | Leverages expanding gas during vacuum |
| Vacuum-sealed pouch | ASTM F2096 | Uses internal pressure to push out leaks |
| Low-headspace tray | ASTM F2096 or dye test | ASTM D3078 often ineffective, unless using modified test (air injection) |
| MAP food packaging | ASTM D3078 | Ideal headspace and material compatibility |
If you’re unsure which to use, start by measuring headspace and reviewing your packaging configuration with a trained validation engineer or packaging specialist.
How Internal Pressurization Affects Your Results
One of the most misunderstood aspects of bubble testing is the role internal pressurization plays in outcome reliability. Too often, QA teams assume that vacuum application alone is enough to “pull out” leaks. But physics doesn’t lie—and poorly pressurized packages often escape detection even when defective.
Here’s what’s actually happening:
During vacuum drawdown, the pressure inside the package becomes greater than the surrounding environment. This forces internal gas outward—pushing it through any weak points. But that only works if there’s enough gas to begin with, and nothing in the product is plugging the path.
Common issues from improper pressurization include:
- False negatives from product plug: Viscous or semi-solid products get forced into small leaks during testing, blocking gas escape
- Low differential pressure: Pre-pressurized packages (e.g. 200 psi) show marginal improvements under vacuum, with only a 7.5% differential gain
- Inadequate headspace: Without sufficient air volume, expansion during vacuum is too weak to force visible bubbles
- Over-tight vacuum draw: Pulling too hard or too fast can rupture marginal seals or mask smaller leaks by collapsing the film inward
Bottom line: The pressure differential is what creates detectable bubble trails. If the internal pressure isn’t calibrated, the test won’t work—even if everything else is perfect.
Step-by-Step: How to Perform a Bubble Test Correctly
QA success depends on process control. Whether you’re in food, pharma, or CPG, skipping steps or guessing pressure thresholds can leave you exposed. Here’s a precise walkthrough of the ASTM D3078 procedure as it should be executed on the production floor.
1. Prepare the Specimen and Fluid
Bring the package and immersion fluid (usually water) to room temperature—around 23°C (73°F). Cold fluid can increase surface tension, reducing bubble visibility. Ensure the package has sufficient internal headspace air or gas. If not, inject air through a sterile needle port.
2. Calibrate Your Vacuum
Conduct preliminary trials to determine the max vacuum the package can tolerate without rupturing. From there, use 75% of that level in production testing. For instance, if 24 inHg causes bursting, your test vacuum should max out at 18 inHg.
3. Submerge and Seal
Place the specimen in the vacuum chamber and fully submerge it in the immersion fluid. Seal the lid tightly and double-check all gaskets, gauges, and tubing for air leaks or obstruction.
4. Apply the Vacuum Slowly
Start the vacuum pump and gradually pull down the pressure. A fast draw can cause the package to rupture prematurely or collapse inward, hiding leaks. Maintain the selected vacuum level for at least 30 seconds to allow bubble formation.
5. Observe Carefully
Watch for a continuous stream of bubbles—this indicates a failure. A few isolated bubbles are usually trapped air and considered a pass or inconclusive (retest may be needed). No bubbles? The package passes.
6. Record Results Immediately
Document the vacuum level, hold time, immersion fluid used, and any observations (e.g., leak location, burst behavior). These details are critical for audits and process control.
Q&A: Bubble Testing Best Practices
What is ASTM D3078?
ASTM D3078 is a bubble emission test used to detect gross leaks in flexible packaging with internal headspace gas by submerging the package in fluid under vacuum.
How long should vacuum be applied in ASTM D3078?
Maintain the vacuum for a minimum of 30 seconds to ensure sufficient time for gas to escape and bubble trails to form.
Can I use ASTM D3078 for vacuum-sealed packages?
Technically, yes. Although ASTM D3078 is not recommended for vacuum-sealed or low-headspace packaging, you can inject air into the package with a needle – which allows you to perform a very similar test to ASTM D3078. Alternatively – Use ASTM F2096.
Why are bubbles not forming during the test?
Possible reasons include insufficient headspace, cold immersion fluid, incorrect vacuum level, or product plugging the leak.
What vacuum level should I use?
Determine the max vacuum the package can withstand, then test at 75% of that level for best results.
Final QA: Repeatability, Documentation, and Audit Readiness
Passing one test isn’t enough. For bubble emission testing to hold up under regulatory scrutiny, your results need to be consistent and traceable. That starts with standardizing procedures and documenting everything.
Best practices include:
- Using the same vacuum levels and hold times across every run
- Equilibrating all specimens and fluid to 23°C
- Labeling every package and recording results in real time
- Performing daily chamber checks and quarterly gauge calibration
- Training operators to distinguish true leaks (steady bubbles) from false positives (sporadic air release)
- Using known-defect control samples to verify test sensitivity
- Creating SOPs that match ASTM D3078 and internal protocols
Auditors look for one thing: consistency. If your team can’t explain why a package passed or failed, you lose credibility—and possibly compliance.
When Not to Use Bubble Testing
It’s tempting to use ASTM D3078 across the board, especially since it’s fast and low-cost. But using the wrong method creates risk.
Avoid bubble testing when:
- The package is vacuum-sealed or tightly packed (unless you modify the package by injecting air)
- Internal product is too viscous (e.g., pastes or gels)
- There’s no headspace gas/air
- High sensitivity leak detection is required
In those cases, switch to ASTM F2096 or consult your package testing provider for alternative methods like helium mass spectrometry or dye ingress.
Final Thought
Bubble testing is only as reliable as the process behind it. Done wrong, it creates a false sense of security. Done right, it becomes one of the most valuable tools in your packaging QA arsenal. Don’t settle for visual guesswork—get it right, under pressure.
