You spot it late — a small wet spot on a pallet that shouldn’t be there. Your team begins opening a few cases and finds a pouch with a tiny break in the seal. One flaw in one pack would not be unusual. But what if it wasn’t only one? What if the same seal issue appeared in the last run, too? Moments like this make QA teams replay their last checks in their heads, wondering whether a fast test could have caught the flaw before the product ever reached a truck.
That’s the moment a package leak detector goes from being another piece of equipment to something that protects your production schedule, your brand reputation, and your end customer. And the part many teams overlook is that a modern leak detector can tell you what you need to know in 30 seconds or less — if you match the test to the right package type.
This guide breaks down the process in plain terms, using real operator scenarios, simple steps, and the same clarity FlexPak brings to every training call.
What a Package Leak Detector Actually Does in 30 Seconds
A package leak detector measures whether unwanted air or gas is escaping from a sealed package. It sounds simple — and at its core, it is — but the speed and accuracy of the result depend on choosing the right test method.
Most package leak detectors work through one of a few mechanisms:
Bubble Emission Testing via Vacuum Pressure:
A flexible package is placed underwater inside a vacuum chamber. When vacuum is applied, leaks show up as visible bubbles. This is known as ASTM D3078 bubble emission.
Internal pressurization:
Air is injected into a sealed pouch submerged underwater. If there’s a leak, air escapes as a steady stream of bubbles. This is ASTM F2096.
Vacuum decay or pressure decay:
Sensors measure pressure changes inside a chamber or inside the test unit itself. These approaches detect very small leak rates and don’t involve water. However – there is no ability to see where the leak is. That’s where Vacuum Decay and Pressure Decay fall short of Bubble Emission and Internal Pressurization.
Altitude simulation:
Tests how a sealed container reacts when external pressure drops — similar to truck or air transport changes.
Because the process is so fast, production teams often run tests at the start of a shift, during changeovers, or whenever a tooling adjustment is made. When matched correctly, these detectors find:
- pinholes in films
- weak seals
- channels hidden within a seal
- leaks from handling damage
- corner failures in sachets
- issues caused by product viscosity or trapped particles
Even leaks smaller than what you can see with the naked eye show up immediately.
Why this matters more than people realize
Industry reports show that packaging defects continue to be a top contributor to food recalls. A large portion of those defects tie back to leaks that were not caught early. When a defect gets missed, the ripple is immediate: wasted time, rework, destroyed finished goods, and customer complaints.
QA managers who adopt routine leak detection often talk about the same relief: “Now we know what’s really happening inside the seal.”
For more detail on the basics, FlexPak explains this simply on our bubble testing blog post:
➡️ https://flexpakinc.com/bubble-testing/
How to Choose the Right Package Leak Test for Your Product
Here’s where most teams get tripped up. They assume all tests find all leaks. They assume headspace doesn’t matter. They assume they can use the same test for a protein pouch, a beverage sachet, and a sterile barrier pack.
Choosing the correct method is the difference between catching a problem early or shipping it without realizing something was wrong.
Below is a simple, expert-backed decision path:
Step 1: Identify your package type
Ask yourself:
- Is it flexible or rigid?
- Is there headspace inside or almost none?
- Is the product liquid, powder, or solid?
- Is the material porous or non-porous?
- Does the seal run straight, or does it have corners/gussets?
Knowing these answers narrows your options fast.
Step 2: Match your package to the correct ASTM method
| Package Type / Condition | Best Test | Why It Works |
| Flexible pouch with headspace | ASTM D3078 | Bubbles show leak points visually. |
| Medical pouches with little/no headspace (Tyvek) | ASTM F2096 | Pressurization creates a clear bubble path. |
| Liquid-filled containers | ASTM D3078 (Dry Chamber) | Vacuum stresses the pack without contamination. |
| Vacuum-sealed packs | VAC inflation + D3078 | Inflation adds air to the package, then ASTM D3078 to expose hidden leaks. |
| Packs shipped at altitude | ASTM D6653 | Simulates pressure changes during transport. |
FlexPak breaks this down further on our testing overview pages:
➡️ https://flexpakinc.com/our-process/
Step 3: Consider sensitivity needs
If you’re testing sterile medical packaging, you may need a more controlled and repeatable test like F2096 or vacuum decay.
If you’re testing snack bags, pouches, flow wraps, food packaging, or any flexible packaging, bubble emission is the industry standard.
Step 4: Think about your operators
If a test requires judgment, training matters.
Bubble tests are fast, but operator technique determines whether small leaks get spotted.
A small story that makes this real
A QA lead at a mid-sized bakery once noticed staling complaints on a high-volume SKU. Visual checks showed nothing. But a quick match to bubble emission testing revealed a recurring tiny pinhole at the bottom weld. This wasn’t an expensive fix — just a sealing temperature adjustment — but without the right test, the issue would have continued for months.
Bubble Emission Testing Explained (ASTM D3078)
This is the test most people imagine when they think about a package leak detector — the clear chamber filled with water and the visual moment where tiny bubbles show the source of the problem.
How the test works
- A flexible package goes into a water-filled chamber.
- A vacuum pulls air out of the chamber.
- If the package has a leak, internal air escapes and bubbles appear.
- Operators watch the origin, pattern, and speed of the bubbles.
In many QA labs, this entire process takes around 30 seconds.
Packages that work best for D3078
- snack bags
- stand-up pouches
- sachets with air or nitrogen headspace
- wet wipe packages
- detergent pod pouches
- flexible medical pouches with some headspace
Packages filled completely with liquid aren’t ideal for this test — there’s simply not enough air to escape.
For a walk-through of the process, see FlexPak’s guide:
➡️ https://flexpakinc.com/how-to-perform-a-bubble-leak-test-your-30-second-solution-to-package-integrity/
Common errors that distort results
Errors usually come down to setup:
- not enough headspace
- water level too low
- vacuum too strong or too weak
- thick liquids blocking leak paths
- packages not fully submerged
- confusing trapped air in folds as real leaks
Operators often say the trickiest part is telling the difference between a real defect and a harmless release of trapped air. The next sections help with that.
How bubble testing compares to other methods
| Method | Sensitivity | Speed | Cost | Operator Skill |
| Bubble Emission | ~250 microns | 30–60 sec | Low | Low |
| Vacuum Decay | ~50 microns | ~30 sec | High | Med |
| Helium Mass Spec | <1 micron | Minutes | Very High | Low |
Bubble tests are simple and visual — but they are not the most sensitive option for extremely small leaks that you would need to identify in Pharma/Medical Industries.
When to Use Internal Pressurization for Food, Pharma, or Medical Packaging
Some packages need a different level of control. If there’s almost no air inside, or if sterility is critical, internal pressurization is usually the better choice.
What the method does
ASTM F2096 involves injecting air into a sealed package submerged underwater. If even a small channel exists anywhere in the seal, you’ll see a consistent bubble trail.
FlexPak details how this works in our medical packaging guides:
➡️ https://flexpakinc.com/medical-package-testing-simplified-how-to-prove-sterile-seal-integrity-without-guesswork/
When F2096 is ideal
Porous or sterile barrier systems:
- medical pouches
- surgical kits
- pharma tray lids
High-stakes seals:
When any leak compromises sterility or shelf life.
A real-world illustration
A medical device facility once conducted only D3078 tests for sterile kits. Results were inconsistent — some seals passed one day and failed the next. When the team switched to internal pressurization, they immediately saw a pattern: a narrow channel forming in the lower left sealing jaw. Without F2096’s controlled pressure, that channel would have continued slipping through.
Why this method prevents false negatives
If a pack has little air inside, bubble emission might show nothing even when a leak exists. Pressurization fills the package with enough air to expose the weakness clearly.
Teams often don’t realize this until they’ve been burned by a false pass.
Common Testing Mistakes That Skew Leak Detection Results
You can use the best package leak detector in the world and still miss leaks if the fundamentals aren’t followed. These mistakes show up in almost every facility at some point.
Mistake #1: Using the wrong ASTM method
Choosing D3078 when headspace is too low is a recipe for false passes.
Choosing F2096 when a product is sensitive to flooding can damage samples.
Mistake #2: Not inflating vacuum-sealed packs
Vacuum packs have almost zero air. If you don’t inflate them before the test, leaks stay hidden.
FlexPak explains how our VAC attachments solve this:
➡️ https://flexpakinc.com/product/vacuum-pack-attachment/
Mistake #3: Inconsistent test setup
Minor variations cause major differences:
- vacuum ramp too fast
- cycle time shortened
- water depth not checked
- sample temperature ignored
- seals wet or contaminated from the line
When a plant switches shifts or rotates operators, this inconsistency grows.
Mistake #4: Misinterpreting bubble behavior
A few bubbles from a fold aren’t a leak.
A steady, repeated stream from the exact same spot is.
This is why visual training is just as important as method selection.
Mistake #5: Skipping routine calibration
Leak detectors drift.
Vacuum chambers age.
Fixtures loosen.
Regular small checks — including reference leaks — keep your data trustworthy.
FlexPak covers this extensively in our “avoid costly mistakes” breakdown:
➡️ https://flexpakinc.com/leak-detector-testing-avoid-these-5-costly-mistakes/
How to Read Leak Patterns and Know Exactly What They Mean
This is the section operators always ask for. Test methods tell you whether there’s a leak. Bubble patterns tell you what kind of leak you’re dealing with — and often how severe it might be.
Pattern 1: No bubbles at all
This usually means a pass — but confirm vacuum and hold time were strong enough.
Pattern 2: A couple of bubbles, then nothing
Likely trapped air in pleats or corners. Retest with a fresh sample to be sure.
Pattern 3: A tight, steady stream from one point
That’s a pinhole or puncture.
You’ll often see it at:
- corners
- spots where product has sharp edges
- film abrasions from line handling
Pattern 4: Multiple bubbles tracing a short line
This is a channel leak inside the seal.
Channels love to hide at areas where:
- temperature wasn’t uniform
- contamination worked its way into the seal
- the sealing jaw had a worn zone
Pattern 5: Large, irregular bubbles along a long seal section
This often indicates a weak or open seal.
The longer the segment, the more likely it is linked to sealing pressure or alignment.
How operators distinguish real leaks from false positives
A real leak produces repeatable bubbles from the same location throughout the full hold.
A false positive shifts location, stops early, or appears during only the pressure ramp.
A quick practice story
A QA technician kept reporting “random leaks” on a powdered drink sachet, but results never repeated. After watching her test, the supervisor realized that an air pocket inside the gusset was releasing during vacuum ramp. When the test was repeated with careful flattening of the gusset, the “leaks” disappeared.
Once the team knew what to watch for, false positives vanished
Comparison Table: Leak Test Methods at a Glance
| Test | Best For | Not Ideal For | Sensitivity | Test Time |
| ASTM D3078 Bubble Emission | Flexible packs with headspace | Fully liquid-filled packs | ~250 microns | 30–60 sec |
| ASTM F2096 Internal Pressurization | Low-headspace packs, sterile barriers | Packs that can’t be submerged | ~250 microns | 30–60 sec |
| ASTM F2338Vacuum Decay | Medical/pharma high sensitivity | Large packages | ~50 microns | ~30 sec |
| ASTM D6653Altitude Simulation | Vacuum packs, shipped goods | All-liquid packs | Detects seal stress/rupture | 30 mins – 1 hr+ |
| ASTM D3078Dry Chamber | Liquid-filled bottles | Rigid trays | Depends on setup | 30–60 sec |
Q&A:
How long should I hold vacuum during a bubble test?
As per the ASTM D3078 standard – once at your desired pressure, hold for at least 30 seconds.
What if no bubbles appear?
Confirm vacuum strength, water depth, and whether the package has enough air to escape.
How deep should the pack be submerged?
Fully covered. Partial submersion hides leaks.
Can I bubble-test a fully liquid pack?
No — use internal pressurization or a dry chamber test.
Why do my results change between operators?
Inconsistent sample prep, vacuum ramp, or viewing angle.
Your Next Step: Test Smarter, Not Harder
If you’re reading this because you’ve had inconsistent leak results, small complaints creeping in, or a recent production shift that brought new sealing issues, that’s the perfect time to reassess your testing setup.
A package leak detector is not about adding work to your day. It’s about removing the worry of missed defects. Whether you need guidance choosing between D3078 and F2096 or want help setting up a test station your team can trust, FlexPak can walk you through the process in a way that’s simple, fast, and built around your packaging line.
➡️ Book a Call with Our Experts (24-hour response):
https://meetings.hubspot.com/gordon92
➡️ Compare testing methods and find the right unit:
https://flexpakinc.com/our-process/
➡️ Request a Quote
https://flexpakinc.com/get-a-quote/
Protect your line. Protect your product. And make leak detection one of the easiest parts of your QA routine.