WHAT IS THE BUBBLE LEAK TEST (ASTM D3078)?
Understand the basics of ASTM D3078 and when this vacuum-based test method is the right fit for your package type.
In 2022, the USDA-FSIS logged 53 meat & poultry recalls, many of which may have been caused by seal failures or compromised flexible packaging which could have been prevented with proper leak detection. For quality control managers and packaging engineers in food, pharma, and medical device industries, the bubble leak test is one of the fastest, most cost-effective ways to spot gross leaks before a product ever leaves the facility.
ASTM D3078 is the standard method used for bubble emission leak testing. This process involves placing a flexible package with headspace gas (air or modified atmosphere) into a vacuum chamber filled with water. When vacuum is applied, pressure inside the package drops, forcing air/gas out through any breach. If bubbles form in the water, there’s a leak. If not, the package is deemed intact.
But it’s not just about seeing bubbles—it’s about knowing what those bubbles mean, when this method makes sense, and what it can’t detect.
When is ASTM D3078 appropriate?
- You’re testing flexible packages with internal headspace (air or gas)
- You need fast, visual confirmation of seal integrity
- You’re screening for defects like pinhole leaks, punctures or open seals
- You’re running batch-level QA for regulated products
When gross leak detection is the goal, bubble emission testing is hard to beat for speed, simplicity, and visual clarity.
Quick Comparison: Bubble Leak Test vs. Other Methods
| Feature | ASTM D3078 (Bubble) | Helium Leak Test | Dye Penetration Test |
| Sensitivity | Medium | High | Low |
| Ease of Use | High | Low | Medium |
| Equipment Cost | Low | High | Low |
| Visual Result | Yes | No | Yes |
| Operator Dependence | Medium | Low | High |
EQUIPMENT YOU NEED FOR A BUBBLE LEAK TEST
A quick checklist of tools required—including vacuum chamber specs, pressure gauges, and packaging media setup tips.
You don’t need a lab full of instruments to perform ASTM D3078—but what you do use has to work reliably and be properly configured. A leaky vacuum chamber or cloudy water can cost you time and trust.
Here’s what’s required:
- Transparent vacuum chamber: Must be strong enough to withstand full atmospheric pressure differential, and fully clear to allow for bubble observation.
- Vacuum-tight cover with gauge: The lid should seal completely and include fittings for a vacuum pump, pressure gauge, and atmosphere release tube.
- Vacuum pump: Creates the pressure differential that draws gas out of the package.
- Pressure regulator: Helps fine-tune vacuum levels so you don’t over- or under-pressurize.
- Test fluid: Tap water works perfect. It should be at room temperature and degassed to avoid bubble confusion.
- Holding fixture or grid: Keeps the package fully submerged without floating.
- Observation lighting: Good lighting around the chamber ensures even faint bubbles aren’t missed.
Maintenance is non-negotiable. Uncalibrated gauges, leaky fittings, or foggy chambers make even the most thorough testing useless.
HOW TO PERFORM THE TEST STEP-BY-STEP
Follow this repeatable process—from sample submersion to vacuum application—to ensure compliant, consistent results.
Start with a clean, sealed, unpunctured flexible package that contains headspace gas or oxygen. Bring both the test sample and water to room temperature (ideally 20–25°C).
Step 1: Set up the chamber
Fill the chamber with water deep enough to fully submerge the package. Place the sample in the center and lower the lid and hold-down plate, submerging the package.
Step 2: Apply vacuum
Seal the lid and slowly apply vacuum. Start with a target of 200–600 mbar absolute pressure—but this should be determined based on your package’s structural limit. Maintain vacuum for at least 30 seconds.
Step 3: Observe
Watch for a continuous stream of bubbles from any part of the package. That’s a leak. A single, small bubble? Possibly trapped air. No bubbles? That’s a pass.
Step 4: Release and record
Release the vacuum, remove the package, and record test results immediately—including test conditions and observations.
Pro tips for accuracy:
- Run preliminary tests to find your ideal vacuum level.
- Keep all conditions—vacuum, time, water temperature—consistent.
- If you’re unsure about a bubble’s cause, retest or escalate.
HOW TO INTERPRET TEST RESULTS ACCURATELY
Learn what qualifies as a failure, how to document results, and when to retest or escalate based on findings.
Results come down to what you see:
- No bubbles = PASS
- Single or sporadic bubble = INCONCLUSIVE
- Steady stream = FAIL
But visual confirmation alone isn’t enough—you need to log all parameters.
Document:
- Vacuum level (mbar, inHg or kPa)
- Hold time (minimum 30 seconds)
- Water temp (°C)
- Package ID
- Leak location (if observed)
- Operator initials and date
- Comments (e.g., re-tested, air bubble observed, repeat failed)
Sample Log:
| Package ID | Vacuum | Hold Time | Temp | Result | Leak Location | Operator | Date |
| 34201 | 400 mbar | 30 sec | 22°C | Pass | N/A | A. Patel | 6/6/25 |
| 34202 | 400 mbar | 30 sec | 22°C | Fail | Side Seal | A. Patel | 6/6/25 |
| 34203 | 400 mbar | 30 sec | 22°C | Inconclusive | Bottom Fold | A. Patel | 6/6/25 |
If there’s ever a doubt—repeat the test. Record everything. When audits happen, this documentation becomes your shield.
COMMON TESTING MISTAKES TO AVOID
Eliminate false positives, seal contamination, and setup issues that can compromise both safety and compliance.
Even experienced QA teams slip up when testing feels routine. Here are some of the biggest (and most expensive) ways to get it wrong:
1. Rushing the vacuum step.
If you apply vacuum too fast, it can rupture the sample. Too slow, and the test becomes inefficient. Stick to a steady ramp-up and hold for the full 30 seconds.
2. Testing packages without headspace.
No internal air? No bubble test. You’ll get false negatives because there’s no pressure differential to push air through leaks. Note: You can modify the package by injecting air through an airhose/needle fixture – ask the FlexPak Team for tips!
3. Not prepping the water.
Cold water has high surface tension. This can actually prevent small leaks from showing visible bubbles. Room temperature water matters.
4. Operator distractions.
Bubble emission is visual. If the operator isn’t attentive/is distracted – this can result in undetected leaks.
5. Poor chamber maintenance.
Foggy windows, leaky gaskets, miscalibrated gauges—these all skew results or obscure visual indicators. Keep the system in top condition.
6. Misreading trapped air.
Some folds or seams trap small air pockets that escape slowly, mimicking a leak. If it doesn’t continue, don’t call it a failure right away.
These errors don’t just cost time. They cost trust, regulatory approval, and sometimes entire shipments. QA isn’t just about passing a test—it’s about having confidence that a pass means something.
