Two ASTM F88 tests can use the same package material and still produce different results.
The reason is not always the testing machine.
Tail orientation, specimen width, grip condition, support technique, seal location, and the way the result is calculated can all change what the force value represents.
That is why a useful ASTM F88 test starts before the specimen is placed in the grips.
A practical test chain looks like this:
Package → Specimen → Technique → Seal Force → Grip → Peel Curve → Failure Mode → Equipment
This guide focuses on that chain: how to run ASTM F88 more consistently, how to recognize questionable results, and how to configure a seal-strength testing system around the actual package.
ASTM F88 at a Glance
ASTM currently lists ASTM F88/F88M-23 as the active standard for measuring seal strength in flexible barrier materials. It covers seals between flexible materials and other flexible, rigid, or semi-rigid materials, measures the force required to separate a sealed test strip, and also identifies the specimen failure mode.
| Item | Practical Answer |
|---|---|
| Standard | ASTM F88/F88M |
| Test purpose | Seal strength of flexible barrier materials |
| Main measurement | Force required to separate the seal |
| Typical results | Maximum seal force and, where applicable, average force |
| Test techniques | Technique A, B and C |
| Critical variables | Tail support, specimen width, grip, alignment, test condition |
| Failure evaluation | Force value + failure mode |
| Typical machine | Low-force tensile / peel testing system |
| ITM-LAB starting platform | RS-8010A |
A useful rule for the whole article is:
Before comparing the numbers, compare the setup.
What Does ASTM F88 Actually Measure?
ASTM F88/F88M measures the mechanical force required to separate a sealed specimen under a defined test condition. The method can be applied to seals produced in the laboratory or taken from commercial packaging.
Typical applications include:
- flexible food packaging,
- medical pouches,
- pharmaceutical packaging,
- laminated barrier materials,
- peelable seals,
- flexible-to-flexible seals,
- and flexible-to-rigid seal structures.
The result is useful for much more than a simple pass/fail check.
Seal strength data can support:
- process validation,
- seal-process development,
- production control,
- supplier comparison,
- material evaluation,
- and package opening-performance studies.
But the force value only becomes meaningful when the test technique and failure mode are known.
A 20 N result caused by clean seal separation is not the same event as a 20 N result caused by film tearing.
ASTM F88 Technique A, B and C
One of the most important parts of ASTM F88 testing is how the specimen tails are handled while the seal separates.
The standard distinguishes three techniques:
Technique A — Unsupported
Technique B — Supported 90° by hand
Technique C — Supported 180°
ASTM notes that part of the measured force can come from bending of the material rather than seal strength alone. Because each support technique changes that bending contribution, the same technique should be used consistently within a test series.
Technique A — Unsupported
Both specimen tails are held in opposing grips.
The seal remains unsupported during the test.
The specimen is therefore free to change orientation as the grips separate.
This is easy to understand mechanically, but bending of the flexible tails still contributes to the overall response.
Technique B — Supported 90° by Hand
The specimen is supported by hand so that the seal remains approximately perpendicular to the specimen tails during separation.
This looks simple, but there is an important practical detail:
“Supported by hand” does not mean “held firmly by hand.”
If one operator only guides the specimen while another pushes or pulls laterally against it, both tests may be labelled Technique B while the mechanical conditions are no longer equivalent.
The operator should maintain the intended orientation without adding unnecessary force to the measurement.
Technique C — Supported 180°
The less flexible tail is supported flat against a rigid alignment plate, while the more flexible tail is folded back 180° and held in the opposing grip.
Again, the package seal may be identical to the one used for Technique A or B.
The specimen mechanics are not.
Why the Technique Changes the Result
Imagine cutting three specimens from the same seal.
Same material.
Same seal width.
Same sealing process.
Same test machine.
Specimen 1 uses Technique A.
Specimen 2 uses Technique B.
Specimen 3 uses Technique C.
If the force values differ, that does not automatically mean the package changed.
Part of the measured force comes from how the flexible material bends during the test. Change the tail support and that contribution changes too. ASTM explicitly warns about this effect.
This creates a simple comparison rule:
Technique A, B and C are not interchangeable datasets.
Before comparing seal-strength results from two suppliers or laboratories, confirm:
Same technique?
Same tail orientation?
Same specimen width?
Same conditioning?
Same reporting method?
If those answers are unknown, “both tested to ASTM F88” is not enough information.
Stronger Is Not Always Better
Seal strength is often discussed as though the highest possible value is automatically the best result.
That is not always true.
A package seal normally has to satisfy two competing requirements:
Stay closed when it should stay closed
and
open when it is intended to open
This is especially relevant for peelable packages.
Think of seal performance as a target window.
Too Weak
Possible concerns:
- opening during handling,
- process inconsistency,
- reduced package robustness.
Target Range
The seal provides the required package security while remaining suitable for its intended opening method.
Too Strong
Possible concerns:
- difficult opening,
- film tearing,
- delamination,
- poor user experience,
- failure somewhere other than the intended seal interface.
The objective is therefore not:
“Make the seal force as high as possible.”
It is:
“Keep the seal force inside the range required by the package design.”
A higher number is only better when the package requirement says it is better.
Seal Strength Is Not the Same as Seal Integrity
ASTM F88 answers:
How much mechanical force is required to separate the seal?
It does not, by itself, tell you whether the package contains:
- a leak,
- a microscopic channel,
- a pinhole,
- an incomplete seal,
- or another integrity defect.
That requires an appropriate integrity or leak test.
ASTM packaging standards treat these as separate questions. F88 addresses mechanical seal strength, while other F02 methods address visual seal evaluation, dye penetration, leak detection and related integrity issues.
A useful distinction is:
| Question | Test Type |
|---|---|
| How strong is the seal? | Seal-strength test |
| Does the package contain a leak or channel? | Integrity / leak test |
A strong seal can still contain a defect. A leak-free seal can still open at an undesirable force.
Both results can matter.
They are not substitutes for each other.
Specimen Preparation: Start With the Package, Not the Machine
A universal testing machine can measure force very accurately.
It cannot decide whether the strip placed in its grips represents the package correctly.
Before testing, define and record:
- specimen location,
- specimen width,
- seal orientation,
- package structure,
- tail direction,
- cutting method,
- conditioning,
- and test technique.
Seal strength can vary across a package.
For production troubleshooting, where the specimen was cut from may matter almost as much as the final force value.
If one section of a seal shows a low result while another section is normal, the question may be related to the sealing process rather than the material itself.
Why Specimen Width Matters
Consider two simplified examples.
Specimen A
Measured force:
30 N
Width:
15 mm
Normalized engineering value:
2.0 N/mm
Specimen B
Measured force:
50 N
Width:
25 mm
Normalized engineering value:
2.0 N/mm
If only the total force is compared:
50 N > 30 N
Specimen B appears much stronger.
Once width is considered:
2.0 N/mm = 2.0 N/mm
the interpretation changes.
The actual reporting convention should follow the applicable ASTM F88 procedure and customer specification, but the engineering lesson is clear:
A force value needs specimen context.
ASTM has also investigated the relationship between different F88 specimen widths in supporting interlaboratory work, which reinforces why width should be controlled when results are compared.
Maximum Seal Force and Average Seal Force Answer Different Questions
A seal-strength test produces a force curve.
That curve may contain:
- an initial peak,
- a stable peel region,
- local fluctuations,
- secondary peaks,
- and final separation.
ASTM F88 recognizes maximum force as an important result and also supports average-force evaluation where applicable.
The two values should not be treated as the same thing.
Maximum Seal Force
This answers:
What was the highest measured force during separation?
For example:
Maximum Force = 28 N
That peak may occur only briefly.
Average Seal Force
This describes the force behavior over a defined region of seal separation.
Consider two packages.
Package A
Large initial peak:
30 N
Then the force falls to:
8–12 N
Package B
Maximum force:
24 N
but most of the peel region remains around:
20–22 N
If only the maximum value is compared:
A looks stronger.
If the full separation behavior is considered:
the picture is different.
One peak does not describe the entire seal.
Read the Curve Before You Copy the Number
Suppose the software reports:
Maximum Seal Force = 25.4 N
Before adding that number to the report, look at the graph.
Curve 1
A relatively stable plateau around 18–22 N.
Curve 2
Repeated jumps between 8 N and 30 N.
Curve 3
A sudden spike followed immediately by zero because the film tore.
All three could contain a peak around 25 N.
They do not represent the same package behavior.
This is one area where automatic software calculations help—but do not replace engineering interpretation.
A clean 20 N plateau tells a different story from a curve that jumps between 8 and 30 N.
During routine QC, a specification may only require a defined number.
During troubleshooting and process development, the curve deserves attention.
Failure Mode: Same Force Does Not Mean Same Failure
ASTM F88 specifically requires identification of the mode of specimen failure.
This is one of the most useful parts of the method.
Seal Peel
The seal separates through the intended sealed region.
This is the most direct case for evaluating seal separation.
Film Tear
The film tears before the seal has fully separated.
Now part of the force is controlled by the packaging material itself.
If the goal is to compare the seal interface, that distinction matters.
Delamination
Layers within a laminate separate.
The weak point may now be the interlayer bond rather than the original seal.
A higher or lower force cannot be interpreted correctly without recording that change.
Material Break
The specimen breaks somewhere outside the intended seal-separation mechanism.
The machine still produces a number.
That does not automatically make the number a clean seal-strength result.
Record what failed—not only how much force was measured.
When Should You Question an ASTM F88 Result?
A completed test is not automatically a useful test.
Several observations deserve a closer look.
| Observation | First Question |
|---|---|
| Peak high, average low | Is one local strong point dominating the result? |
| Very unstable curve | Seal variation or specimen slip? |
| Film tears before seal opens | Are we still measuring seal separation? |
| Delamination occurs | Is laminate bond controlling the failure? |
| Break occurs beside grip | Is the grip damaging the specimen? |
| Same package, two labs disagree | Same technique and tail handling? |
| Operator-to-operator difference | Same clamping and Technique B support? |
If the first three specimens all fail beside the same jaw edge, stop there.
Cutting another ten specimens is unlikely to fix the grip.
Inspect the setup first.
Grip Selection: Enough Force to Hold, Not Enough to Damage
Flexible packaging creates a difficult gripping problem.
The specimen may be:
- thin,
- smooth,
- soft,
- extensible,
- laminated,
- or easily damaged.
The grip must hold the specimen without becoming part of the failure mechanism.
Too Little Clamping
Result:
Slippage
Too Much Local Pressure
Result:
Premature jaw-area failure
Poor Alignment
Result:
Uneven separation
Wrong Jaw Surface
Result:
Inconsistent holding
The strongest possible grip is not automatically the best grip.
The correct grip is the one that keeps the specimen stable throughout the defined test.
Mechanical or Pneumatic Grips?
Both can work.
The better choice depends on testing frequency and specimen behavior.
Mechanical Grips
Good candidates for:
- R&D,
- lower test volume,
- varied specimen types,
- laboratories where frequent fixture changes are required.
They are simple and flexible.
But operator tightening can introduce some variation.
Pneumatic Grips
Useful when:
- specimen volume is high,
- repeated clamping is required,
- operator-to-operator repeatability is important,
- controlled clamping pressure is valuable.
For example, a production laboratory testing hundreds of pouch specimens per day may value repeatable pneumatic clamping more than a laboratory testing five development specimens once a week.
Pneumatic is not automatically “more ASTM compliant.”
It solves a workflow and repeatability problem.
Load Cell Selection: Measure the Force You Actually Have
ASTM F88 is often a low-force application.
Suppose the seal force is expected to be:
15–25 N
and the machine frame is rated to:
5 kN
The question:
“Is 5 kN enough?”
does not help much.
Of course it is enough.
The useful question is:
Which force-measurement range is appropriate around 15–25 N?
The frame gives the machine overall capacity.
The load cell determines how the working force is measured.
A practical sequence is:
Package → Width → Expected Force → Technique → Load Cell → Grip → Machine
A larger load cell is not automatically a better load cell.
What About ASTM F88 Test Speed?
This is a common search question, but it should not be answered by copying one number into every laboratory procedure.
The correct speed should follow the applicable ASTM F88/F88M revision and the test method/specification being used.
The practical equipment question is:
Can the machine reproduce the specified rate consistently while the specimen is separating?
The practical laboratory question is:
Were the results being compared generated using the same rate and technique?
If one supplier changes technique, specimen handling and test speed at the same time, it becomes difficult to identify which variable caused the difference.
For publication and compliance work, use the exact values and procedure defined in the licensed standard and customer specification rather than relying on a secondary summary.
A Typical ASTM F88 Equipment Inquiry
A customer writes:
“We need an ASTM F88 seal strength tester for medical pouches.”
That identifies the application.
It does not define the machine configuration.
We would still want to know:
Package construction?
Flexible-to-flexible or flexible-to-rigid?
Specimen width?
Expected seal force?
Technique A, B or C?
Maximum force, average force or both?
How much does the film stretch?
How many specimens per day?
Does the material slip easily?
Now assume the answers are:
Package: Flexible medical pouch
Specimen Width: 15 mm
Expected Seal Force: 10–30 N
Testing Volume: 120 specimens/day
Technique: Defined by customer procedure
Results: Maximum + Average Force
The equipment discussion now becomes:
Suitable Low-Force Load Cell
Packaging Grip
Pneumatic Clamping where appropriate
Technique-Specific Support
Force-Curve Analysis
This is much more useful than asking only:
“Which machine complies with ASTM F88?”
ASTM F88 Equipment Configuration Matrix
| Requirement | Main Concern | Practical Configuration |
|---|---|---|
| Routine packaging QC | Repeatability | RS-8010A + suitable load cell + packaging grips |
| Seal force below ~30 N | Low-force measurement | Load cell selected around working force |
| High-volume medical pouch QC | Operator variation | Pneumatic gripping where appropriate |
| Very smooth film | Slippage | Specimen-specific jaw surface |
| Fragile / thin film | Grip damage | Controlled clamping pressure |
| Technique B / C | Tail orientation | Correct support arrangement |
| High-elongation specimen | Machine travel | Confirm usable travel |
| Process development | Full behavior | Curve analysis + failure-mode recording |
| Multi-package laboratory | Flexibility | Interchangeable grips / load cells |
The equipment is not selected from ASTM F88 alone.
It is selected from:
ASTM F88 + your package.
RS-8010A for ASTM F88 Seal Strength Testing
Once the application is defined as a relatively low-force seal separation test requiring controlled motion, suitable gripping and force-curve analysis, the RS-8010A Universal Testing Machine becomes the natural ITM-LAB starting platform.
A typical configuration can include:
RS-8010A
Appropriate Low-Force Load Cell
Mechanical or Pneumatic Packaging Grips
Technique-Specific Support
Force–Displacement Software
The machine's maximum capacity is not the main selling point for this test.
If your seal opens at 18 N, the system should measure that 18 N range well.
If another package requires 180 N, the configuration can be adjusted accordingly.
Configure the test system around the package—not the package around the machine.
ASTM F88 vs F2029 vs F1921 vs F2824
These standards all relate to package seals, but they answer different engineering questions.
| Standard | Main Question |
|---|---|
| ASTM F88/F88M | How strong is the finished seal? |
| ASTM F2029 | How can laboratory heat seals be produced for heat-sealability studies? |
| ASTM F1921/F1921M | How strong is the seal while it is still hot? |
| ASTM F2824 | What force is required to remove the entire lid from certain round rigid or semi-rigid containers? |
ASTM F2029 explicitly directs users to F88 for testing seal strength and separates hot-tack evaluation into F1921. ASTM F88 itself distinguishes its strip-based seal-strength method from F2824 whole-lid removal testing.
This creates a useful standards chain:
Create laboratory seal
→ ASTM F2029
Evaluate finished seal strength
→ ASTM F88
Evaluate hot seal / hot tack
→ ASTM F1921
Different questions.
Different procedures.
Potentially different equipment.
ASTM F88 Troubleshooting Matrix
| Symptom | Check First |
|---|---|
| Specimen slips | Grip surface / clamping |
| Break beside jaw | Grip pressure / jaw edge |
| High specimen-to-specimen scatter | Seal location / width / preparation |
| Unstable curve | Seal consistency / slip / failure mode |
| Force unexpectedly high | Technique / specimen width / seal structure |
| Force unexpectedly low | Seal quality / cutting / gripping |
| Film tears | Record failure mode; determine what controls failure |
| Laminate separates | Evaluate delamination |
| Two laboratories disagree | Compare technique, speed, width, conditioning |
| Operator results differ | Technique B support / grip consistency |
Use the symptom to narrow the investigation.
Do not start every troubleshooting session by recalibrating the machine.
Before Pressing START: ASTM F88 Checklist
Confirm:
□ Standard revision / customer method
□ Package structure
□ Seal location
□ Specimen width
□ Clean specimen edges
□ Conditioning
□ Technique A / B / C
□ Correct tail orientation
□ Test rate
□ Expected force range
□ Suitable load cell
□ Appropriate grip
□ Appropriate clamping pressure
□ Specimen alignment
□ Support arrangement if required
□ Maximum / average result requirements
□ Failure-mode recording
□ Reporting units
The specimen being clamped into the machine means the physical setup has started.
It does not mean the test definition is complete.
FAQ
- What is ASTM F88?
ASTM F88/F88M is a standard test method for measuring seal strength in flexible barrier materials. It measures the force required to separate a sealed specimen and identifies the specimen failure mode.
- What is the difference between ASTM F88 Technique A, B and C?
Technique A is unsupported. Technique B keeps the seal supported at approximately 90° by hand. Technique C uses a supported 180° configuration. These techniques create different bending conditions and should not be treated as interchangeable datasets.
- Is a higher ASTM F88 seal strength always better?
No. The desired seal strength depends on package requirements. Peelable packages may require enough strength for distribution and storage but not so much that opening becomes difficult or the packaging material fails first.
- What is the ASTM F88 test speed?
Use the test rate defined by the applicable ASTM F88/F88M revision and customer or laboratory procedure. Do not assume one secondary-source value applies to every test configuration.
- What specimen width is used for ASTM F88?
Use the specimen dimensions defined by the applicable procedure and package specification. Width should be controlled because it influences the force result and comparison between specimens.
- What is the difference between maximum and average seal force?
Maximum force is the highest force measured during the test. Average force characterizes the force over a defined portion of seal separation. One local peak and a consistently strong seal can therefore produce different interpretations.
- What does film tear mean in ASTM F88?
It means the packaging film becomes part of the failure mechanism. The force result should be interpreted together with this failure mode rather than automatically treating it as clean seal-interface separation.
- Does ASTM F88 test seal integrity?
No. ASTM F88 evaluates mechanical seal strength. Leak and channel detection require appropriate integrity test methods.
- What load cell should be used for ASTM F88?
Choose a load-cell range suitable for the expected seal force rather than simply matching the maximum capacity of the testing frame.
- Can RS-8010A perform ASTM F88 testing?
Yes. RS-8010A can be configured with suitable low-force load cells, grips, support fixtures and software for ASTM F88 seal-strength applications.
Information to Send When Requesting an ASTM F88 Testing Solution
Instead of sending:
“We need an ASTM F88 tester.”
send:
Package Material: ______
Seal Structure: ______
Flexible-to-Flexible / Flexible-to-Rigid: ______
Specimen Width: ______
Expected Seal Force: ______
Technique: A / B / C
Required Result: Maximum / Average / Both
Expected Elongation: ______
Test Volume: ______ specimens/day
Grip Preference: Mechanical / Pneumatic / Recommend
Other Packaging Standards: ______
That information allows the supplier to configure:
Load Cell → Grip → Support → Travel → Software → Machine
instead of guessing from a standard number.
Conclusion: ASTM F88 Is a Test System, Not Just a Pull Test
ASTM F88 looks simple because the specimen is small and the force is often low.
That simplicity is deceptive.
Change Technique A to Technique C and the specimen mechanics change.
Support Technique B differently and the result can change.
Ignore specimen width and two force values may be compared incorrectly.
Look only at maximum force and important peel behavior can disappear.
Ignore the failure mode and a film tear may be reported as though it were clean seal separation.
A reliable ASTM F88 test therefore follows this sequence:
Package
↓
Specimen
↓
Technique
↓
Expected Force
↓
Grip
↓
Load Cell
↓
Curve
↓
Failure Mode
↓
Testing Machine
For conventional flexible-packaging seal-strength testing, the ITM-LAB RS-8010A provides a practical starting platform when configured with the appropriate low-force sensor, packaging grip and technique-specific support.
The goal is not simply to buy a machine labelled:
ASTM F88 Compatible
The goal is to reproduce the required ASTM F88 condition on the actual package you need to evaluate.
