Last updated: March 2026
A pharmaceutical QA manager called us last month with a question that comes up more often than you’d think: is pressure decay or vacuum decay the right method for her blister pack line?
The answer wasn’t simple. But the reasoning was clear.
That’s the problem with most pressure decay content. It’s written for engineers testing engine blocks, valve assemblies, and cast metal components. If you’re testing flexible pouches, rigid trays, or pharmaceutical packaging, the industrial framing doesn’t translate — and you’re left guessing.
This guide does the translation. It covers what pressure decay leak testing actually is, how the test cycle works, how it compares to vacuum decay and bubble emission testing in a packaging context, and which package types and scenarios it suits best.
What Is Pressure Decay Leak Testing?
Pressure decay leak testing is a nondestructive method that detects leaks by monitoring pressure loss inside a sealed test chamber over time. The package or test chamber is pressurized to a set level through a sealed external fixture — no puncturing required. Once the pressure source is isolated, any leak causes pressure to drop. A precision transducer measures that drop and records a pass or fail.
No water submersion. No visual inspection. No package destruction. The result is quantitative: a pressure decay rate that either falls within your validated acceptance range or triggers a fail.
In packaging applications, pressure decay is typically used for rigid and semi-rigid containers where internal pressurization is practical — bottles, trays, blister packs, and similar formats. It sits alongside vacuum decay (ASTM F2338) and bubble emission testing (ASTM D3078) as one of several nondestructive methods available for package leak testing.
How Pressure Decay Testing Works: The Five-Phase Cycle
The test follows a five-phase sequence. Understanding each phase helps when setting parameters and interpreting results.
1. Pressurization. The package or test chamber is pressurized to a predetermined level using a regulated air supply. The target pressure is established during method validation for your specific package type.
2. Stabilization. A short stabilization period allows temperature and pressure to equalize inside the test system. This phase matters more than most people give it credit for. Skipping or shortening it is the most common source of false failures — thermal expansion from filling causes pressure readings to drift even in a perfectly sealed package.
3. Isolation. The pressure source is disconnected. The system is now closed.
4. Measurement. A precision transducer monitors the sealed chamber over the test period, typically seconds to a few minutes depending on the package and required sensitivity. Any pressure drop beyond the acceptance threshold indicates a leak.
5. Result. The system outputs a pass or fail based on the measured decay rate against your validated acceptance criterion. Some systems log decay rate data for trending and audit trail purposes.
The entire cycle can complete in well under a minute for most packaging applications, making pressure decay practical for high-throughput production environments where inline or at-line testing is required.
Pressure Decay vs. Vacuum Decay: Same Principle, Different Direction
Pressure decay and vacuum decay are conceptually similar. Both are nondestructive. Both use a sealed test chamber and a pressure transducer to detect leaks. Both produce quantitative results.
The core difference is direction.
Pressure decay applies positive pressure inside the package and monitors for outward pressure loss. Vacuum decay (ASTM F2338) draws a vacuum around the outside of the package and monitors for pressure rise inside the chamber, which signals gas or liquid escaping from the package.
Vacuum decay is better suited to:
- Flexible pouches where internal pressurization would cause deformation
- Packages where the seal geometry makes introducing a pressurized air supply inconsistent
- Any format where external chamber contact is easier to control than internal pressurization
Pressure decay is better suited to:
- Rigid and semi-rigid containers that can withstand controlled internal pressure
- Formats where a tight, repeatable external chamber seal is harder to achieve
- Applications where the container’s closure-to-container interface is the primary integrity concern
| Pressure Decay | Vacuum Decay (ASTM F2338) | |
| Pressure direction | Positive pressure inside package | Vacuum applied outside package |
| Detects leaks? | Yes | Yes |
| Destructive? | No | No |
| Best for | Rigid and semi-rigid containers | Flexible and rigid nonporous packages |
| Quantitative result? | Yes | Yes |
| ASTM standard | No single dedicated packaging standard | ASTM F2338 |
One important note on vacuum decay sensitivity: ASTM F2338 sensitivity figures are validated for specific package types and test conditions. The validated detection limits for nonlidded rigid trays, porous barrier lidded trays, rigid nonporous bottles, and glass syringes differ from one another. Don’t apply those figures across package formats without validation.
FlexPak’s equipment is designed around bubble emission testing (ASTM D3078) and related packaging test methods. If vacuum decay per ASTM F2338 is the specified method for your program, our team can help you map the right approach to your format and compliance requirements.
Pressure Decay vs. Bubble Emission Testing: When Each Method Wins
Bubble emission testing (ASTM D3078) and pressure decay serve different purposes. They’re not direct substitutes, but knowing where each excels helps when you’re building a testing program.
Bubble emission testing submerges the package in fluid, draws a vacuum, and reveals leaks as a visible stream of bubbles escaping the package. It works for flexible packages with headspace gas, requires no complex chamber tooling, and gives you the exact location of the leak. It’s also nondestructive. The trade-off: it requires headspace gas to work reliably, it’s a qualitative pass/fail method, and it doesn’t produce a quantitative leak rate.
Pressure decay produces a quantitative result, which makes it easier to establish and document acceptance criteria, trend data over time, and prove consistency for validation purposes. It works for packages with no headspace gas. But it won’t tell you where on the package the leak is, and it requires package-specific chamber tooling for every format you test.
| Pressure Decay | Bubble Emission (ASTM D3078) | |
| Headspace gas required? | No | Yes, for reliable detection |
| Result type | Quantitative (decay rate) | Qualitative (pass/fail, visual) |
| Leak location identified? | No | Yes |
| Destructive? | No | No |
| Package-specific tooling? | Yes | Minimal |
| Best for | Rigid containers, validation programs, audit trail | Flexible packages, production spot checks, QA programs requiring leak location |
| Speed | Seconds to minutes | ~30 seconds with FlexPak equipment |
The honest answer for most food and CPG packaging operations: bubble emission testing covers the majority of practical QA needs. It’s fast, visual, nondestructive, and requires no format-specific tooling investment. Brands like Nestlé, Hershey’s, and Smucker’s rely on it for exactly this reason.
FlexPak’s equipment runs ASTM D3078 bubble emission tests with results in around 30 seconds. Package submerged, vacuum drawn, escaping gas produces a visible bubble stream at the exact leak location. No format-specific tooling required, and operators run the same validated recipe every time. One point worth noting for operations running vacuum-sealed or low-headspace packages: those packages contain little to no free headspace gas, which means D3078 can false-pass even when a real leak is present. FlexPak’s VAC Attachment solves this by injecting a brief air shot into vacuum-sealed packages before testing, giving them the headspace D3078 needs to work. It’s a small accessory that makes a meaningful difference for snack foods, processed meats, and any SKU that ships with an oxygen barrier.
For repeatability across shifts, FlexPak’s FPFAT controller stores up to 24 validated bubble emission test recipes. Once your team dials in the vacuum setpoint, hold time, and draw rate for a given SKU, operators run the exact same protocol every time without touching any calibration settings. That matters when you need to demonstrate consistency for a validation program, a customer audit, or a regulatory review.
Pressure decay becomes the stronger choice when quantitative data is required, when the package format makes bubble emission impractical, or when a pharmaceutical or medical device validation program specifically requires a documented quantitative method.
Which Package Types Are Right for Pressure Decay Testing?
Pressure decay is best matched to packages that can accept a controlled internal pressure without deforming and where an external chamber seal can be reliably maintained around the package geometry.
Rigid bottles and containers. Pressure decay is a standard method for bottles and jars where internal pressurization is straightforward and the container geometry is consistent enough for repeatable chamber tooling.
Blister packs and formed trays. Pharmaceutical and medical device blister packaging is one of the most common pressure decay applications. The rigid formed cavity pressurizes consistently, and the method produces the quantitative, documented results that validation programs typically require.
Semi-rigid containers with closures. Containers with threaded or snap-fit closures where the closure-to-container seal is the primary integrity concern can suit pressure decay well, particularly where the closure geometry makes vacuum chamber sealing inconsistent. For threaded closure gross leak testing, ASTM D5094 is also worth evaluating alongside pressure decay.
Packages with no headspace gas. Vacuum-sealed products, liquid-filled packages, or any format where there is minimal headspace gas cannot be reliably tested with bubble emission — ASTM D3078 requires headspace gas to produce bubbles. Pressure decay doesn’t have this limitation.
Where pressure decay typically doesn’t fit:
- Highly flexible pouches where internal pressurization causes deformation that affects test results
- Applications where leak location is needed for production troubleshooting
- High-volume food packaging lines where format-specific tooling investment and changeover time per SKU is impractical
Practical Considerations Before Choosing Pressure Decay
Method validation is the starting point. The acceptance criterion — what decay rate constitutes a pass — must be established and validated for your specific package type before pressure decay means anything. This isn’t plug-and-play. Limits don’t transfer between package formats, and the validation work happens before any production testing begins.
Tooling is the second consideration. Every package format requires a fitted test chamber or insert. For operations running several different package types, this adds capital cost and changeover complexity that bubble emission testing simply doesn’t have. If your line runs five different pouch formats, the tooling investment multiplies accordingly.
The leak location gap matters for troubleshooting. Pressure decay tells you a leak exists. It won’t tell you which seal bar created it. If your QA program needs to identify which seam is failing so operators can adjust the machine, you’ll need a visual method alongside it. That’s typically where bubble emission comes back into the picture, even for programs where pressure decay is the primary quantitative method.
On the other side of the ledger: quantitative data is a genuine advantage in regulated industries. The ability to log a decay rate for every test supports audit trails, trending analysis, and validation documentation in a way that a qualitative pass/fail result can’t replicate.
For pharmaceutical and medical device programs, it’s also worth knowing that ASTM F2096 (internal pressurization followed by gross leak detection) is a separate standard with its own scope and sensitivity data. FlexPak’s FPIPA accessory enables ASTM F2096 testing on the same base FlexPak unit that runs D3078 — one machine, both standards, without capital investment in a second platform. If your pharmaceutical program requires F2096 and you’re already running D3078, that’s a useful consolidation. FlexPak’s equipment ships with full IQ/OQ/PQ documentation, which means the installation qualification, operational qualification, and performance qualification records your validation team needs are already prepared.
FlexPak’s equipment focuses on bubble emission (ASTM D3078) and related package integrity test methods including ASTM F2096, D6653, D4991, D5094, and D4169. If pressure decay is the right fit for your package and compliance requirements, our team can help you understand where it sits relative to the methods we support — and whether a combined approach makes sense for your program.
Frequently Asked Questions
What is pressure decay leak testing? Pressure decay leak testing is a nondestructive method that pressurizes a sealed package or test chamber, isolates the pressure source, then monitors for pressure loss over a set time period. A pressure drop beyond the validated acceptance threshold indicates a leak. It produces a quantitative result and requires no water submersion.
What is the difference between pressure decay and vacuum decay testing? Both methods use a sealed chamber and pressure transducer to detect leaks nondestructively. Pressure decay applies positive pressure inside the package and monitors for outward pressure loss. Vacuum decay (ASTM F2338) applies vacuum outside the package and monitors for pressure rise caused by escaping gas or liquid. Vacuum decay generally suits flexible packages better; pressure decay suits rigid and semi-rigid containers that can be internally pressurized.
Is pressure decay testing destructive? No. Pressure decay testing is nondestructive when applied within validated pressure limits for the package type. The package is pressurized but not punctured, submerged, or otherwise altered.
Does pressure decay testing work for flexible pouches? Generally not. Internal pressurization can cause the pouch to deform, which affects the reliability of the pressure measurement. For flexible packages containing headspace gas, bubble emission testing (ASTM D3078) is typically the more practical choice. For flexible packages with no headspace gas, vacuum decay (ASTM F2338) is worth evaluating.
What industries use pressure decay leak testing for packaging? Pressure decay is most commonly used in pharmaceutical and medical device packaging, where quantitative results and documented validation are typically required. It also appears in rigid food and beverage container testing, cosmetics packaging, and any application involving rigid or semi-rigid containers where a quantitative, nondestructive leak test is needed.
What’s the difference between pressure decay and ASTM F2096? They’re related but distinct. ASTM F2096 is a specific standard for gross leak detection using internal pressurization — the package is internally pressurized, then checked visually or with a bubble emission method for leaks. Pressure decay is the underlying measurement technique used in various methods. F2096 is the published standard with defined procedure, sensitivity data, and precision statements. FlexPak’s FPIPA accessory enables ASTM F2096 testing.
When should I use bubble emission instead of pressure decay? For most food, CPG, and flexible packaging operations, bubble emission testing (ASTM D3078) is the faster, simpler, more practical choice. It requires no format-specific tooling, identifies leak location, and runs in about 30 seconds. The case for pressure decay is strongest when your program requires a quantitative result, when your package format can’t accommodate bubble emission reliably, or when your validation documentation specifically requires a quantitative nondestructive method.
If your package is rigid, your program needs quantitative documentation, and you’re running pharmaceutical or medical device validation, pressure decay earns its place.
For most food, CPG, and flexible packaging operations, bubble emission and related package integrity test methods get you there faster, with less tooling investment and better leak location capability.
Not sure which method fits your format? Get a quote in 24 hours — we’ll work through the right method combination for your package type and compliance requirements.
About the Author: Gordon Bruce, Sales and Application Expert, FlexPak Inc. Gordon has spent years helping food, pharmaceutical, and industrial manufacturers select and implement leak detection and package integrity testing programs. He works directly with QA teams to match testing methods to real package formats, compliance requirements, and production environments.