Minimum Order Quantity (MOQ): 1 pallet (typically 125–250+ bulk bags)
To specify a polyethylene liner on an FIBC purchase order, do not simply write “FIBC with poly liner.” State that the FIBC requires a polyethylene liner and reference the approved liner specification and drawing. Then define the liner construction, material, thickness when critical, dimensions, top and bottom configuration, closure, attachment or positioning method, filling interface, air-displacement requirements, discharge interface, product-contact requirements, and any applicable moisture, cleanliness, chemical, or electrostatic requirements. The liner also needs to be specified as part of the complete FIBC: product, particle size, bulk density, payload, Safe Working Load (SWL), safety factor, body construction, coated or uncoated outer fabric, seams, top, bottom, lift loops, dimensions, pallet, printing, packing, and revision. “Poly liner” is not a specification. It is the beginning of one.
Here is a purchase order line that looks specific but really isn’t:
“Heavy-duty FIBC with 3 mil poly liner.”
Okay.
What polyethylene?
Loose insertion or form fit?
What liner dimensions?
How is the liner positioned?
What does the liner top look like?
What does the liner bottom look like?
How is it closed?
What product is going inside?
Why does the product need a liner?
How fine is it?
Is moisture the problem?
Is dust the problem?
How fast are you filling?
Where does displaced air go?
How is the product discharged?
Can the liner move toward the outlet?
What outer FIBC construction is required?
What SWL?
What safety factor?
Which approved revision?
Those details determine whether you receive a packaging system that works—or a plastic bag stuffed inside another bag.
A polyethylene liner is a flexible film component positioned inside the structural woven polypropylene FIBC.
The two components perform different jobs.
The outer FIBC primarily provides:
Structural strength.
Payload support.
Lift loops.
Body construction.
Handling capability.
Top and bottom architecture.
The polyethylene liner may provide:
Additional fine-particle containment.
Moisture protection.
Product-contact separation.
Contamination control.
Additional internal barrier performance.
Do not confuse the two.
A useful starting point is:
Liner: Polyethylene Liner Per Approved FIBC Specification and Drawing
If you have a controlled liner specification, make the wording more precise:
Liner: Polyethylene Liner Per Approved Liner Specification, FIBC Drawing and Current Revision
Then define the critical liner characteristics.
There are many ways to construct and install a liner.
Two suppliers can both quote:
FIBC with polyethylene liner
and provide significantly different packaging systems.
One liner may:
Fit closely.
Stay positioned.
Fill consistently.
Discharge cleanly.
Another may:
Balloon.
Twist.
Wrinkle.
Shift.
Block the outlet.
Trap product.
Same description.
Very different result.
Before specifying the liner, finish this sentence:
“The polyethylene liner is required because…”
Possible answers include:
Fine-particle containment.
Moisture protection.
Product-contact separation.
Contamination control.
Cleanliness.
Chemical compatibility.
Another defined barrier requirement.
This single question prevents a lot of bad specifications.
Safe from what?
Every liner should solve a defined problem.
Otherwise you may add:
Cost.
Complexity.
Filling time.
Airflow restrictions.
Discharge problems.
Residual product.
Without gaining meaningful performance.
The liner specification should begin with the product.
Identify the actual material whenever practical.
Do not rely on:
“Powder.”
“Granules.”
“Chemical.”
“Food product.”
“Dry material.”
Those descriptions are too broad.
Particle size matters when the liner is being used for containment.
Extremely fine particles behave differently from coarse granular material.
Do not look only at average particle size.
The smallest particles may determine:
Dust.
Sifting.
Product migration.
Containment requirements.
Particle shape can affect:
Liner wear.
Flowability.
Discharge.
Puncture risk.
Abrasion.
Does the product create dust during:
Filling?
Handling?
Transportation?
Discharge?
Document what actually happens.
Bulk density affects:
Required FIBC volume.
Target payload.
Filled geometry.
SWL.
Pallet fit.
Warehouse cube.
Transportation.
The liner needs to work inside the complete loaded package.
State the intended product weight.
Do not use:
“Fill completely.”
Volume and weight are different constraints.
The outer FIBC carries the structural load.
Specify the required SWL.
Do not assume the polyethylene liner adds structural carrying capacity.
Specify the appropriate safety factor for the intended use.
The liner does not replace or increase the FIBC’s required structural safety factor.
The liner exists inside a particular body design.
Specify:
Circular.
U-panel.
Four-panel.
Baffle.
Another approved construction.
This matters.
Possible combinations include:
Uncoated woven polypropylene + polyethylene liner.
Coated woven polypropylene + polyethylene liner.
These packages can behave differently.
A useful purchase-order description might state:
Fabric: Uncoated Woven Polypropylene Per Approved FIBC Specification
Liner: Polyethylene Liner Per Approved Liner Specification and Drawing
The uncoated outer fabric may provide greater natural breathability.
But remember:
Air trapped inside the liner still needs a path out.
A purchase order might state:
Fabric: Coated Woven Polypropylene Per Approved FIBC Specification
Liner: Polyethylene Liner Per Approved Liner Specification and Drawing
This combination may provide additional barrier performance.
It can also make air management more important.
Do not leave this open to interpretation.
State the approved liner construction.
For example:
Liner Construction: Loose-Insertion Polyethylene Liner Per Approved Drawing
Or:
Liner Construction: Form-Fit Polyethylene Liner Per Approved Drawing
Call or Text us at 832.400.1394
A loose-insertion liner should be defined beyond the word “loose.”
Control critical:
Material.
Thickness.
Dimensions.
Top.
Bottom.
Positioning.
Attachment when applicable.
Closure.
Filling interface.
Discharge interface.
A form-fit liner should reference the approved geometry and drawing.
Its purpose is generally to more closely follow the shape of the outer FIBC.
Control the features that affect:
Positioning.
Filling.
Product distribution.
Discharge.
“Polyethylene” itself may not be enough for technically demanding applications.
If material composition affects:
Product compatibility.
Food contact.
Temperature performance.
Barrier requirements.
Process requirements.
Specify the approved material.
If liner thickness is an important performance requirement, control it.
But do not assume:
Thicker = better.
Thickness needs to balance:
Durability.
Flexibility.
Barrier requirements.
Filling.
Discharge.
Cost.
“Heavy duty” is subjective.
Use measurable requirements.
The liner needs to fit the FIBC and process.
Too much excess material can contribute to:
Wrinkles.
Folds.
Bunching.
Residual product.
Discharge problems.
Poor fit can create different problems.
Use an approved liner drawing.
This is extremely important.
The liner top needs to work with the actual filling process.
Define whether the liner uses an approved:
Open configuration.
Spout configuration.
Extended top.
Closure.
Other design.
Do not confuse liner top with FIBC top.
The outer FIBC may use:
Open top.
Duffle top.
Filling spout.
The liner inside may have its own configuration.
Both should be defined.
Ask:
How does the filling equipment connect to the FIBC?
How does it connect to the liner?
Is the liner secured during filling?
Can it move?
Does the filling head require specific dimensions?
Document the answers.
If production throughput matters, communicate the required filling rate.
This becomes particularly important with lined FIBCs.
This is one of the most important requirements in the entire liner specification.
Product enters.
Air leaves.
Where?
If nobody can answer that question, the lined FIBC has not been fully engineered for filling.
Some powders carry substantial air into the package.
That can create:
Liner inflation.
FIBC ballooning.
Product backup.
Dust.
Longer filling cycles.
If the approved liner or filling system requires a particular venting arrangement, control it.
Do not assume the outer woven FIBC automatically solves air displacement.
Watch the liner during production testing.
Some movement may be acceptable.
Excessive ballooning may not be.
Define how the liner should sit inside the FIBC.
Poor positioning can cause:
Wrinkles.
Twisting.
Uneven filling.
Outlet blockage.
Residual product.
If the approved design requires the liner to be attached, tabbed, tied, glued, or otherwise controlled, document that requirement precisely.
Do not leave attachment method to assumption.
Some applications may require liner removability.
Others may prioritize secure positioning.
If this matters operationally, specify it.
The liner bottom needs to match the discharge method.
This is where many vague liner specifications fail.
The outer FIBC might use:
Flat bottom.
Discharge spout.
Duffle bottom.
Other approved construction.
The liner needs to work with it.
If the FIBC uses a discharge spout, define how the liner interfaces with that outlet.
The liner should not unexpectedly:
Collapse.
Block the outlet.
Restrict product.
Get pulled into the discharge stream.
If bottom discharge is not required, make sure the liner design works with the actual unloading process.
Wide-opening discharge can create significant liner movement.
Evaluate:
Film bunching.
Product trapping.
Uncontrolled liner movement.
Closure.
Operator handling.
Does the material:
Flow freely?
Bridge?
Cake?
Clump?
Compact?
Interlock?
The liner’s internal surface and geometry can affect discharge.
Does the customer need:
Rapid discharge?
Controlled discharge?
Partial discharge?
Metered flow?
The liner needs to support the process.
Where does the product go?
Hopper?
Mixer?
Conveyor?
Bin?
Process vessel?
Other container?
The FIBC and liner should be designed around the actual receiving system.
This is especially important for high-value materials.
Product can remain trapped in:
Liner folds.
Corners.
Wrinkles.
Outlet areas.
If residual product matters, define and test acceptable performance.
Do not simply write:
“Moisture resistant.”
Define the actual exposure.
Consider:
Humidity.
Storage duration.
Transportation.
Temperature changes.
Potential direct water exposure.
Required barrier performance.
A polyethylene liner may improve moisture protection.
That does not automatically make the complete FIBC waterproof.
The package includes:
Liner openings.
Closures.
Interfaces.
Outer fabric.
Top.
Bottom.
Potential damage points.
If gas or vapor containment is critical, define the performance requirement.
Do not assume a standard polyethylene liner creates an airtight package.
If cleanliness is the reason for the liner, define what that means for the application.
Consider:
Product-contact surfaces.
Manufacturing environment.
Handling.
Packing.
Storage.
Installation.
Do not write:
“Poly liner — food grade.”
Without defining the applicable requirements.
The complete product-contact system needs to meet the required specification.
If the product is chemically aggressive or compatibility is uncertain, verify the liner material.
Do not assume all polyethylene films perform identically with every product.
Communicate actual filling and storage temperatures when they are unusual or technically relevant.
Abrasive material can wear the liner during:
Filling.
Settling.
Handling.
Transportation.
Discharge.
Sharp material can potentially:
Puncture.
Cut.
Abrade.
Stress.
The liner.
Tell the supplier what the liner is actually facing.
A standard polyethylene liner should not automatically be assumed appropriate for every electrostatic environment.
If static control matters, specify the required complete FIBC/liner system separately.
A polyethylene liner does not automatically make an FIBC UN certified.
If regulated dangerous goods are involved, the complete approved packaging configuration matters.
Changing the liner can potentially mean changing the packaging configuration.
The liner does not make structural seams irrelevant.
Define appropriate:
Structural seams.
Containment requirements.
Top seams.
Bottom seams.
Control:
Loop style.
Loop location.
Loop dimensions.
Equipment compatibility.
The liner does not determine how the FIBC is lifted.
Check:
Body.
Loops.
Top.
Bottom.
Filling equipment.
Discharge equipment.
Facility clearance.
Control the approved dimensions and tolerances.
Loaded dimensions may determine whether the FIBC works in the real operation.
Measure:
Width.
Length.
Height.
Footprint.
When those values are operationally important.
Do not write:
“Standard pallet.”
Define the pallet requirement.
A liner can influence product distribution, but it is only one part of filled geometry.
Test the complete package.
Consider:
Loaded footprint.
Loaded height.
Storage duration.
Humidity.
Temperature.
Handling.
Product protection.
The complete FIBC may experience:
Vibration.
Settling.
Humidity changes.
Temperature changes.
Forklift handling.
Pallet movement.
Long transit periods.
The liner needs to survive that entire process.
Define:
Product identification.
Company information.
Handling instructions.
Warnings.
Lot information.
Traceability.
Other required markings.
How should lined FIBCs arrive?
Consider:
Folding.
Palletization.
Liner positioning.
Liner protection.
Orientation.
Quantity per pallet.
The liner should arrive ready for efficient use.
Call or Text us at 832.400.1394
| Specification | What to Define |
|---|---|
| 📦 Product | Actual material |
| 🔬 Particle characteristics | Size, fines, shape, dust |
| ⚗️ Bulk density | Actual value or approved range |
| ⚖️ Payload | Intended fill weight |
| ⚖️ SWL | Required Safe Working Load |
| 🛡️ Safety factor | Required intended-use classification |
| 🧶 Body | Circular, U-panel, four-panel, baffle, etc. |
| 💨 Outer fabric | Coated or uncoated woven PP |
| 🛍️ Liner | Polyethylene |
| 📐 Liner style | Loose insertion, form fit, approved alternative |
| 🧪 Liner material | Approved composition when critical |
| 📏 Thickness | Controlled when critical |
| 🔝 Liner top | Filling-compatible configuration |
| ⬇️ Liner bottom | Discharge-compatible configuration |
| 📌 Positioning | Approved installation/attachment |
| 🌬️ Air management | Required filling/venting behavior |
| 💧 Moisture | Required barrier performance |
| 🧼 Cleanliness | Applicable product-contact requirements |
| ⚡ Static | Separate electrostatic requirements |
| 🪡 Seams | Outer FIBC requirements |
| 🪢 Loops | Style and dimensions |
| 📐 FIBC dimensions | Empty and critical filled dimensions |
| 🪵 Pallet | Actual pallet requirement |
| ⚙️ Filling | Equipment and production rate |
| 🔻 Discharge | Method and receiving equipment |
| 🏷️ Printing | Approved artwork |
| 📦 Packing | Empty-FIBC packing |
| 📄 Revision | Controlled specification |
A simple controlled liner line could read:
Liner: Polyethylene Liner Per Approved Liner Specification and FIBC Drawing [Revision]
A more complete FIBC description could read:
FIBC — [Approved Body Construction] / [Coated or Uncoated] Woven Polypropylene Fabric / [Approved Top] / [Approved Bottom] / Polyethylene Liner Per Approved Specification / [Required SWL] / [Required Safety Factor] / [Lift Loop Configuration] / Per Approved FIBC Specification and Drawing [Revision]
Body Construction: [Approved FIBC Construction]
Outer Fabric: [Coated or Uncoated] Woven Polypropylene Per Approved Specification
Liner: Loose-Insertion Polyethylene Liner Per Approved Liner Drawing
Liner Material: Per Approved Specification
Liner Thickness: Per Approved Specification
Liner Top: Per Approved Filling Configuration
Liner Bottom: Per Approved Discharge Configuration
Liner Positioning: Per Approved Drawing
SWL: Required Safe Working Load
Safety Factor: Required Intended-Use Classification
Top: Approved Outer FIBC Top
Bottom: Approved Outer FIBC Bottom
Lift Loops: Per Approved Drawing
Dimensions: Per Approved Drawing
Revision: Current Approved Revision
Body Construction: [Approved FIBC Construction]
Outer Fabric: [Coated or Uncoated] Woven Polypropylene Per Approved Specification
Liner: Form-Fit Polyethylene Liner Per Approved Liner Drawing
Liner Material: Per Approved Specification
Liner Thickness: Per Approved Specification
Liner Geometry: Form Fit to Approved FIBC Construction
Liner Top: Per Approved Filling Configuration
Liner Bottom: Per Approved Discharge Configuration
Liner Positioning: Per Approved Drawing
SWL: Required Safe Working Load
Safety Factor: Required Intended-Use Classification
Top: Approved Outer FIBC Top
Bottom: Approved Outer FIBC Bottom
Lift Loops: Per Approved Drawing
Dimensions: Per Approved Drawing
Revision: Current Approved Revision
Avoid:
“Poly liner.”
“Bag with liner.”
“Heavy-duty liner.”
“Thick liner.”
“Moisture-proof liner.”
“Food-grade liner.”
“Same liner as last time.”
“Standard poly liner.”
These phrases leave too much room for interpretation.
Before releasing the PO, confirm:
Common mistakes include:
Writing only “with liner.”
Writing only “poly liner.”
Assuming all polyethylene liners are the same.
Using “heavy duty” instead of measurable requirements.
Assuming thicker is automatically better.
Never defining why the liner is needed.
Ignoring particle size.
Ignoring the fine fraction.
Ignoring dust.
Ignoring bulk density.
Ignoring target payload.
Ignoring outer FIBC construction.
Ignoring coated versus uncoated fabric.
Ignoring liner material.
Ignoring liner geometry.
Ignoring liner dimensions.
Ignoring liner top.
Ignoring liner bottom.
Ignoring liner positioning.
Ignoring attachment.
Ignoring filling equipment.
Ignoring production rate.
Ignoring air displacement.
Ignoring aerated product.
Ignoring liner inflation.
Ignoring outer FIBC inflation.
Ignoring product backup.
Ignoring discharge.
Ignoring liner movement during discharge.
Ignoring residual product.
Ignoring moisture requirements.
Assuming the liner makes the package waterproof.
Assuming the liner makes the package airtight.
Assuming the liner makes the package dustproof.
Assuming the liner makes the package food grade.
Assuming the liner makes the package UN certified.
Ignoring static requirements.
Ignoring chemical compatibility.
Ignoring temperature.
Ignoring abrasion.
Ignoring sharp particles.
Ignoring pallet fit.
Ignoring warehouse conditions.
Ignoring nationwide transportation.
Ordering from an old photograph.
Writing “same as previous order.”
Allowing specification changes to live only in email.
Failing to control revisions.
Make sure suppliers are quoting the same:
Product application.
Particle characteristics.
Bulk density.
Payload.
SWL.
Safety factor.
Body construction.
Outer fabric.
Top.
Bottom.
Seams.
Polyethylene liner material.
Liner construction.
Liner thickness when critical.
Liner dimensions.
Liner top.
Liner bottom.
Liner positioning.
Air-management requirements.
Discharge requirements.
Loops.
FIBC dimensions.
Pallet requirements.
Printing.
Packing.
Revision.
Otherwise, the lowest quote may simply be the least complete specification.
Do not approve it by holding the liner up in the air and saying:
“Looks good.”
Put it inside the actual FIBC.
Then fill it.
Use the actual product whenever practical.
Use the intended payload.
Use the real filling equipment.
Run at production speed.
Watch:
Liner inflation.
Liner movement.
Wrinkling.
Twisting.
Folding.
Air displacement.
FIBC inflation.
Product backup.
Dust.
Product containment.
Measure total filling cycle time.
Measure:
Width.
Length.
Height.
Overhang.
Stability.
Allow representative settling.
Measure again.
Evaluate:
Humidity.
Temperature.
Storage duration.
Product protection.
Liner position.
Filled geometry.
Evaluate:
Vibration.
Settling.
Temperature changes.
Humidity changes.
Handling.
Pallet movement.
Then inspect the liner again.
Use the real receiving equipment.
Observe:
Product flow.
Liner movement.
Outlet blockage.
Bridging.
Surging.
Dust.
Spillage.
Residual product.
Operator intervention.
Measure discharge time.
Compare:
FIBC cost.
Liner cost.
Filling labor.
Filling cycle time.
Product loss.
Dust cleanup.
Moisture-related damage.
Rejected product.
Pallet utilization.
Warehouse cube.
Transportation utilization.
Discharge labor.
Residual product.
Downtime.
Annual volume.
The cheapest liner is not necessarily the lowest-cost liner.
Start with the product.
Define:
Particle size.
Fine-particle content.
Particle shape.
Bulk density.
Flowability.
Dust behavior.
Moisture sensitivity.
Abrasion.
Sharpness.
Temperature.
Chemical compatibility.
Static considerations when applicable.
Target payload.
Then define why the liner exists.
Is it for:
Fine-particle containment?
Moisture protection?
Product-contact separation?
Contamination control?
Cleanliness?
Another barrier requirement?
Now define the outer FIBC:
SWL.
Safety factor.
Body construction.
Coated or uncoated fabric.
Seams.
Top.
Bottom.
Loops.
Dimensions.
Pallet.
Then define the polyethylene liner:
Material.
Loose-insertion or form-fit construction.
Thickness when critical.
Dimensions.
Top configuration.
Bottom configuration.
Positioning.
Attachment when applicable.
Closure.
Filling interface.
Air-management requirements.
Discharge interface.
Then write the controlled requirement:
Liner: Polyethylene Liner Per Approved Liner Specification, FIBC Drawing and Current Revision.
Now test the complete package.
Actual product.
Actual payload.
Actual filling equipment.
Actual production speed.
Actual pallet.
Representative settling.
Representative warehouse conditions.
Representative nationwide transportation.
Actual receiving equipment.
Measure:
Filling cycle time.
Air displacement.
Liner inflation.
Liner movement.
Dust.
Product loss.
Filled geometry.
Moisture performance.
Discharge time.
Outlet interference.
Residual product.
Operator intervention.
Then calculate total economics.
Once the design works, lock it down.
Assign:
Internal item number.
Approved drawing.
Approved liner specification.
Approved FIBC specification.
Revision.
Because “poly liner” tells your supplier almost nothing about how that liner needs to perform.
A good purchase order does not merely say that a liner exists.
It tells everyone exactly what liner belongs inside the FIBC, why it is there, how it interfaces with filling and discharge, and which controlled design must be supplied every time you reorder.
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