Somewhere between your sealing equipment and your customer’s kitchen, a leak happens.
Maybe it’s a tiny channel in a heat seal that looked perfect on the line.
Maybe it’s a pinhole in the film no one noticed.
Air leak testing exists to find those problems before customers do. But with several different test methods available, many teams end up unsure which one actually fits their packaging, their risk level, and their production reality.
The method that works well for pharmaceutical blister packs can be the wrong choice for snack bags.
The most sensitive test might be too slow for your line.
And the easiest system to buy might miss the failures that actually matter.
The goal of this guide is simple:
help you match the right air leak test method to your packaging so testing supports production instead of getting in the way.
What Is an Air Leak Test and Why It Matters
An air leak test checks whether a sealed package allows air or gas to move through it under controlled conditions.
All leak tests follow the same basic idea:
Create a pressure difference between the inside and outside of the package.
Then look for proof that gas is escaping or entering through a defect.
Different methods create that pressure difference in different ways, and they detect leaks differently. But they all answer the same question:
Does this package still protect what’s inside?
Why that matters depends on your product:
- In food packaging, leaks allow oxygen and moisture in, shortening shelf life and raising spoilage risk.
- In modified-atmosphere packaging, a leak defeats the entire purpose of the gas flush.
- In pharmaceutical and medical packaging, a leak compromises sterile barriers and product safety.
In every case, a leak means the package has failed its most basic job.
Visual inspection catches some problems. But small seal channels and pinholes that affect real-world performance are often invisible to the eye. Air leak testing fills that gap between what looks fine and what actually protects the product.
And compared to the cost of complaints, returns, and recalls, leak testing is one of the least expensive quality controls you can add.
Types of Air Leak Tests for Flexible Packaging
There isn’t one “best” air leak test. There are several tools, each built for a different kind of packaging problem.
Understanding the differences makes choosing much easier.
Bubble emission testing (ASTM D3078)
The package is submerged in water inside a vacuum chamber.
Vacuum is applied.
If there is a leak, air escapes and forms visible bubbles.
This is the most widely used production-floor leak test for flexible packaging. It is fast, visual, and shows exactly where a leak is located.
It is designed to find gross leaks and seal failures, not ultra-micro leaks.
Vacuum decay testing (ASTM F2338)
The package is placed in a sealed chamber.
A vacuum is pulled.
The system monitors whether pressure changes over time.
If pressure drifts, gas is moving through a leak.
This method produces quantitative results and can detect smaller defects than visual bubble testing. It’s commonly used for pharmaceutical and medical packaging and anywhere documentation and higher sensitivity are required.
Pressure decay testing
The package is pressurized internally.
The system monitors whether pressure drops.
This method is often used for rigid containers and packages that can hold internal pressure without deforming.
Internal pressurization with bubble detection (ASTM F2096)
Air is introduced into the package.
The package is submerged.
Escaping air forms bubbles at leak sites.
This is frequently used in medical and pharmaceutical packaging, especially where sterile barriers are involved and internal pressurization is preferred.
Altitude simulation testing (ASTM D6653)
Packages are placed in a chamber where pressure is reduced to simulate air transport or high-elevation shipping.
This test does not measure “leak size.”
It evaluates whether packages maintain integrity under real pressure changes that occur in distribution.
It is especially important for products that fly or ship through mountainous regions.
Helium leak testing
Helium is introduced and specialized sensors detect helium escaping through extremely small defects.
This is a high-sensitivity method used primarily for high-value pharmaceutical and medical applications. Equipment cost and complexity limit its use in most food and consumer goods plants.
How Bubble Emission Testing Works
Bubble emission testing deserves special attention because it remains the most practical air leak test for food, snack, and consumer goods packaging.
It is fast.
It is visual.
And it fits real production workflows.
Here’s how it works in practice.
Step 1: Prepare the package and chamber
The package must contain some internal gas.
Vacuum-sealed or liquid-filled packages usually require an air-injection fixture.
The chamber is filled with clean, room-temperature water for consistent viewing.
Step 2: Submerge and seal
The package is fully submerged and restrained so it doesn’t float when vacuum is applied.
Step 3: Apply vacuum
Vacuum is applied at a controlled rate to a validated setpoint based on the package.
The vacuum is held long enough for defects to reveal themselves.
Step 4: Observe
A real leak appears as a continuous stream of bubbles from one location.
Pinholes form fine steady streams.
Seal channels trace along seams.
Weak seals produce broad bubbling.
Short, random bubbles that stop quickly are often trapped air, not leaks.
Step 5: Release and document
Vacuum is released gradually.
Results are recorded.
Failed samples are retained for investigation.
A full test typically takes about 30 seconds once the chamber is loaded.
When to Use Each Air Leak Test Method
The right method depends on four things:
- Package type
- Headspace
- Product risk
- Distribution conditions
Here is a practical way to think about the options:
| Test Method | ASTM Standard | What it’s best at | Typical use |
| Bubble emission | D3078 | Fast, visual detection of gross leaks and seal failures | Flexible food, snack, meat, pet food packaging |
| Vacuum decay | F2338 | Higher sensitivity, quantitative pass/fail | Pharma, medical, high-risk packaging |
| Internal pressurization | F2096 | Gross leak testing without relying on headspace | Medical pouches, sterile trays |
| Altitude simulation | D6653 | Simulating air and high-altitude shipping stress | National distribution, air freight |
| Helium testing | — | Ultra-high sensitivity defect detection | Critical pharmaceutical and medical devices |
Use bubble emission when you need speed, visibility, and location of defects.
Use vacuum decay or helium when very small defects matter.
Use altitude simulation when failures appear only after shipping.
Common Air Leak Test Mistakes (and How to Avoid Them)
Most testing problems don’t come from bad equipment.
They come from small habits.
Testing packages without headspace
Bubble tests need internal gas. Tight vacuum packs won’t bubble unless air is introduced.
Applying vacuum too aggressively
Fast pressure drops can rupture good packages and create confusing results.
Inconsistent test settings
Different vacuum levels or hold times produce different outcomes. Lock parameters into SOPs.
Poor chamber condition
Cloudy windows, worn gaskets, and dirty water hide defects and reduce repeatability.
Operator distraction
Bubble testing is visual. Someone must actually watch.
Lack of calibration and maintenance
Drifting gauges and leaking chambers quietly invalidate results.
Setting Up Air Leak Testing on Your Production Floor
Implementing air leak testing doesn’t require a lab.
It requires clarity.
Step 1: Define what you’re protecting
Which packages matter most?
Which failures would hurt the most?
Step 2: Choose equipment that fits production
Chamber size must match packages.
Controls should support consistent test cycles.
Documentation should fit audit needs.
Step 3: Write simple procedures
Vacuum level
Hold time
Pass/fail definitions
Retest rules
Step 4: Train on patterns, not buttons
Operators should recognize what real leaks look like.
Step 5: Integrate testing into decisions
Who stops the line?
Who isolates product?
Who trends results?
Step 6: Maintain and verify
Leak testers are measurement tools.
Treat them like scales and thermometers.
Final Takeaway
The right air leak test method is the one that fits:
- your packaging
- your risk
- your distribution reality
- and your production pace
For most flexible food and consumer packaging, bubble emission testing remains the fastest way to expose the failures that actually drive complaints and recalls.
It shows leaks clearly.
It fits into daily QA routines.
And it gives teams immediate, actionable answers.
When air leak testing becomes part of normal production instead of a special event, leaks stop being surprises. They become signals.
And signals are problems you can fix.