Views: 0 Author: Site Editor Publish Time: 2026-07-20 Origin: Site
An FIBC label may show two prominent values:
MAX SWL = 1,000 kg
SF = 5:1
These figures answer different questions. The Safe Working Load tells the user how much product the bag is certified to carry in service. The Safety Factor describes the relationship between the SWL and the final load achieved during the applicable cyclic top-lift test.
A 1,000 kg FIBC with a 5:1 safety factor must never be filled with 5,000 kg of product. Its maximum permitted payload remains 1,000 kg.
The distinction matters when specifying, purchasing, filling, lifting, reusing, and inspecting FIBC bags. Misreading either value can lead to overloading, unjustified reuse, incorrect supplier comparisons, or a false assumption that a commercial bag is approved for dangerous goods.
Under ISO 21898:2024 for FIBCs carrying non-dangerous goods:
Marking | Practical meaning | What it does not mean |
|---|---|---|
SWL 1,000 kg | The maximum load the certified FIBC may carry in service is 1,000 kg. | The bag should always be filled to exactly 1,000 kg. |
SF 5:1 | The bag is classified as a single-trip FIBC and must meet the applicable cyclic top-lift test program, including a final load at five times SWL. | The bag may carry five times its SWL or be emptied and refilled. |
SF 6:1 | The bag is classified as a standard-duty reusable FIBC and must meet a more demanding cyclic top-lift test program, including a final load at six times SWL. | The bag can be reused indefinitely, repaired after damage, or automatically used for dangerous goods. |
SF 8:1 | The bag is classified as a heavy-duty reusable FIBC under the standard. | Every application needs an 8:1 bag or that a higher ratio solves all handling risks. |
The operating limit is always the marked SWL. The safety factor is not additional payload capacity.
The Safe Working Load, normally abbreviated as SWL, is the maximum load that an FIBC is certified to carry in service.
If the label states:
MAX SWL = 1,000 kg
the contents placed in the bag must not exceed 1,000 kg. The figure refers to load carried, not the bag’s internal volume and not the combined breaking strength of its individual lifting loops.
SWL should be established for the complete bag design, including:
Body fabric
Coating or lamination
Panel construction
Lifting loops
Loop attachment
Reinforcement
Seams and sewing thread
Top and bottom construction
Closures
Liner, where its presence affects the tested configuration
Intended filling height and filled shape
Changing one of these components can affect whether the original SWL and test evidence remain applicable.
A supplier may describe an FIBC as a “one-ton bag,” but this phrase is not a controlled specification. The buyer should confirm the actual SWL shown in the approved drawing, test documentation, and finished marking.
Likewise, a 1,500-liter bag does not automatically have a 1,500 kg SWL. Liters or cubic meters describe volume, while SWL describes mass.
The relationship depends on the product’s bulk density:
Required product volume = target payload ÷ bulk density
For example, 1,000 kg of material with a settled bulk density of 750 kg/m³ requires approximately:
1,000 ÷ 750 = 1.33 m³
Additional space may be required for the filling profile, headspace, closure, aeration, and product settlement. The resulting bag must provide sufficient usable volume without exceeding either its designed filling height or marked SWL.
A low-density product may fill the bag before reaching its SWL. A high-density product may reach the SWL while much of the apparent volume remains unused. Neither situation permits the operator to ignore the weight limit.
Under ISO 21898:2024, the safety factor is based on the integer quotient between the final load reached in the cyclic top-lift test and the SWL, rounded down.
In simplified form:
Safety factor = final cyclic top-lift test load ÷ SWL, rounded down to a whole number
For a bag with an SWL of 1,000 kg:
Final test load | Calculated quotient | Safety factor classification |
|---|---|---|
4,800 kg | 4.8 | 4:1 |
5,000 kg | 5.0 | 5:1 |
5,200 kg | 5.2 | 5:1 |
6,000 kg | 6.0 | 6:1 |
A result of 4.8 cannot be rounded up and presented as 5:1. Similarly, reaching 5.2 times SWL does not make the design a 6:1 FIBC.
This definition is more precise than saying that the safety factor is simply the bag’s “breaking strength.” The ratio is connected to a prescribed test process performed on a controlled FIBC design. It is not permission to reproduce the test load in a warehouse, filling line, or transport operation.
A 5:1 FIBC is classified as a single-trip bag under ISO 21898:2024.
“Single-trip” means the bag is designed and intended for one filling only. It may pass through several handling stages while filled, such as factory movement, warehousing, container loading, transport, unloading, and final discharge. However, once emptied, it is not intended to be refilled for another service cycle.
For the cyclic top-lift test, a single-trip design is subjected to:
30 cycles at two times its SWL
A final cycle at five times its SWL
For a 1,000 kg SWL bag, the prescribed loads correspond to:
Cyclic loading at 2,000 kg equivalent
A final loading cycle at 5,000 kg equivalent
The test evaluates the complete lifting system and bag body under controlled conditions. To pass, the design must avoid failures such as loss of contents, a lifting device ceasing to support its load, or deterioration that makes the FIBC unsafe for transport or storage.
The 5,000 kg figure belongs to the qualification test. The permitted service payload remains 1,000 kg.
A 5:1 FIBC should not be:
Emptied and refilled
Sold as a reusable bag
Reconditioned for another product movement
Reused merely because it appears clean
Reused after replacing the liner
Patched or structurally repaired for another filling
Assigned a new SWL after use without an approved design and testing process
Visual appearance is not enough to determine residual strength. Fabric, seams, loops, coating, and UV stabilization may have deteriorated without an obvious external failure.
A 5:1 design may be suitable when:
The product is non-dangerous
Only one filling and discharge cycle is planned
The SWL matches the actual maximum payload
The bag construction fits the filling and handling system
The intended product does not create unaddressed abrasion, cutting, chemical, or temperature risks
Electrostatic and hygiene requirements have been evaluated separately
The design has applicable test evidence
The finished bag carries the correct marking
Selecting a 5:1 bag is not inherently a lower-safety decision. It is appropriate when the application genuinely requires a single-trip FIBC and the complete design meets the relevant requirements.
Under ISO 21898:2024 for non-dangerous goods, a 6:1 FIBC is classified as a standard-duty reusable bag.
It is designed and intended for a limited number of fillings and discharges. The standard does not assign one universal number of permitted trips to every 6:1 bag.
The acceptable number of uses depends on the approved design, contents, handling system, exposure, inspection process, supplier instructions, and condition of the individual bag.
A standard-duty reusable FIBC is subjected to:
70 cycles at four times its SWL
A final cycle at six times its SWL
For a 1,000 kg SWL design, this corresponds to:
Cyclic loading at 4,000 kg equivalent
A final loading cycle at 6,000 kg equivalent
This is substantially more demanding than the 5:1 single-trip test program. It supports classification as a standard-duty reusable FIBC, but it does not create an operating limit of 6,000 kg.
The bag should be reused only within a controlled system that defines:
Permitted contents
Maximum payload
Filling and discharge method
Lifting equipment
Storage conditions
Transport route
Inspection responsibility
Rejection criteria
Cleaning requirements
Trip or use records
End-of-life decision
Under ISO 21898:2024, a reusable FIBC should be used with the same type of contents as in its first use. Reuse with a different type of material is outside that conformity basis.
A standard-duty reusable FIBC should not be reused if damaged. This category is not structurally repairable. Replacing a removable liner is not considered a repair, but a new liner does not restore weakened fabric, loops, seams, or reinforcement.
A bag can become unsuitable before reaching a planned trip limit because of:
Cut or punctured fabric
Broken tapes in the weave
Frayed or abraded loops
Damaged loop attachment
Open, loose, or stretched seams
Chemical attack
Heat exposure
UV degradation
Moisture-related contamination
Hard product residues
Uncontrolled cleaning
Forklift damage
Dragging
Product leakage
Missing or unreadable labels
Conversely, the absence of visible damage does not authorize reuse unless the bag was designed, marked, documented, and managed as a reusable FIBC.
Comparison point | 5:1 FIBC | 6:1 FIBC |
|---|---|---|
ISO 21898 class | Single-trip | Standard-duty reusable |
Intended fillings | One filling only | Limited number of fillings and discharges |
Typical operating model | One-way product movement | Controlled reuse system |
Cyclic top-lift program | 30 cycles at 2 × SWL | 70 cycles at 4 × SWL |
Final test cycle | 5 × SWL | 6 × SWL |
Maximum service payload | The marked SWL | The marked SWL |
Refill after discharge | No | Only when the approved reuse conditions are satisfied |
Structural repair | Not applicable | Not permitted for a damaged standard-duty bag |
Contents during reuse | Not applicable | Same type of contents as the first use |
Inspection before another use | Not applicable for refilling because reuse is prohibited | Required as part of the controlled reuse program |
Dangerous-goods approval | Not established by the 5:1 marking | Not established by the 6:1 marking |
Unlimited service life | No | No |
The correct choice therefore depends on the intended service category, not on the assumption that the higher number is always better.
ISO 21898:2024 also recognizes heavy-duty reusable FIBCs with an 8:1 safety factor.
This category is designed for multiple fillings and discharges and can be repairable under controlled conditions. Its cyclic top-lift program includes:
70 cycles at six times SWL
A final cycle at eight times SWL
The standard defines heavy-duty reusable FIBCs as repairable in a way that restores tensile strength across the repair to at least that of the original construction.
An 8:1 design should not be selected simply because it has the highest ratio. The buyer still needs to establish whether repair, return logistics, inspection, cleaning, traceability, and repeated use are operationally practical. Electrostatic behavior, contamination control, product compatibility, and dangerous-goods requirements remain separate decisions.
A safety-factor test creates a controlled performance margin. It does not make overloading acceptable.
There are several reasons for this distinction.
Cyclic top-lift testing is performed on identified samples under defined conditions. The result applies to the qualified FIBC type and the permitted design range.
It does not prove that:
Every production bag has been individually tested to the final load
A used or damaged bag retains the original test margin
A modified bag remains covered
Any product can be carried
Any lifting method is acceptable
The bag can tolerate uncontrolled shock loading
The test load can be treated as a second working limit
Production control is required to keep delivered bags consistent with the tested construction.
The laboratory test does not excuse poor handling. Forces may become concentrated when:
Only some loops are used
Loops are twisted
Forklift tines are too short, sharp, or closely spaced
A bag is lifted at an unapproved angle
The load is unbalanced
The bag catches on surrounding equipment
A suspended bag is accelerated, stopped, or swung abruptly
The filled product shifts during lifting
The bag is dragged or pulled sideways
A 6:1 bag does not make an unsafe lifting method acceptable.
Woven polypropylene and other components can be affected by sunlight, heat, chemicals, abrasion, fatigue, contamination, and physical damage. The safety-factor marking identifies the qualified design category; it is not a real-time measurement of the remaining strength of an individual bag.
A frequent mistake is to use the 5:1 or 6:1 safety factor to estimate how many filled bags can be stacked.
These are different properties.
The safety factor is derived from cyclic top-lift performance. Permitted stacking must be determined through the applicable compression or stacking assessment and stated separately on the FIBC marking.
A bag marked SF 6:1 is not automatically safe for a six-high stack. The label may permit fewer bags, or it may prohibit stacking entirely.
Stacking decisions must also consider:
Filled-bag stability
Product settlement
Bag footprint
Floor condition
Pallet condition
Warehouse environment
Duration of storage
Vibration and transport
Moisture exposure
Local operating procedures
Never calculate permitted stack height by multiplying or dividing the SWL and safety factor.
The 5:1 or 6:1 rating does not indicate whether the FIBC is Type A, B, C, or D.
Electrostatic suitability depends on the product, minimum ignition energy, surrounding atmosphere, filling and discharge process, liner, conductive components, grounding system, and applicable electrostatic test requirements.
A 6:1 Type A bag does not become safe in a combustible atmosphere merely because it has a higher top-lift safety factor. Mechanical strength and electrostatic protection address different hazards.
The required FIBC type should be specified independently from SWL and service category when developing a custom FIBC design.
No. A commercial 6:1 safety-factor statement does not, by itself, establish approval for transporting dangerous goods.
Dangerous-goods flexible IBCs are governed by a separate regulatory design-type system. Their requirements can include:
Permitted FIBC code
Packing group
Maximum permissible load
Approved contents or product scope
Top-lift testing
Drop testing
Tear testing
Topple testing
Righting testing
Stacking testing
Required UN marking
Manufacturing controls
Inspection and record requirements
The dangerous-goods top-lift framework applies a load relationship of six times the maximum permissible load to flexible IBCs. However, passing or claiming a six-times top-lift load alone does not complete the UN test program.
Likewise, an ISO 21898 standard-duty reusable bag marked 6:1 is not automatically approved for dangerous goods. Buyers sourcing UN-certified FIBCs should verify the complete UN design-type marking and test evidence against the material, packing group, route, and applicable transport regulations.
The two uses of “six times” must not be treated as interchangeable approvals.
A compliant label should allow the operator and buyer to connect the physical bag to its approved design and test basis.
For a non-dangerous-goods FIBC under ISO 21898:2024, important fields include:
Label field | What to verify |
|---|---|
Manufacturer | The name and address match the approved supplier and production records. |
Manufacturer’s reference | The reference uniquely identifies the FIBC type. |
MAX SWL | The value is sufficient for the required payload and matches the drawing and test report. |
SF | The ratio matches the intended single-trip or reusable class. |
Permitted stacking | The maximum stacking arrangement is stated separately from SF. |
Test number and date | The records can be traced to the correct design type. |
Approved laboratory | The test facility is identified. |
Test standard | The applicable edition is shown. |
FIBC class | The bag is identified as single-trip, standard-duty reusable, or heavy-duty reusable. |
Manufacture date | The physical bag can be traced to its production period. |
Handling information | Required instructions and pictograms are legible. |
Special treatment | Coating, lamination, stabilization, or electrostatic treatment is identified where applicable. |
The values should be fixed for the approved FIBC type. A generic label containing several SWLs or safety factors to be selected informally creates uncertainty about which design was actually supplied.
Suppose the label states:
SWL: 1,000 kg
SF: 5:1
Class: Single-trip
Permitted stacking: 1 + 2 bags
The correct interpretation is:
Maximum product load: 1,000 kg
One filling only
The bag cannot be refilled after discharge
The cyclic top-lift qualification includes a final load at five times SWL
The stacking limit is determined by the separate stacking marking, not by 5:1
Suppose the label states:
SWL: 1,000 kg
SF: 6:1
Class: Standard-duty reusable
Permitted stacking: 1 + 3 bags
The correct interpretation is:
Maximum product load remains 1,000 kg
The design is intended for a limited number of fillings and discharges
Reuse requires controlled inspection and the same type of contents
A damaged bag cannot be repaired and returned to service as a standard-duty reusable FIBC
The permitted stack is four bags in total, not six
The marking does not establish UN approval
The required SWL should be based on the highest permitted net payload, not only the average batch weight.
Consider:
Target fill weight
Filling-system accuracy
Allowed process variation
Product bulk density
Product aeration and settlement
Bag volume and designed filling height
Transport or customer weight limits
Handling-equipment capacity
Applicable regulatory limits
If a filling line targets 980 kg but can produce bags weighing up to 1,025 kg, an FIBC marked with an SWL of 1,000 kg is not protected by its 5:1 or 6:1 safety factor. The process must be controlled so that the payload never exceeds the marked SWL, or the bag and associated handling system must be specified for an appropriate higher SWL.
Increasing the bag’s SWL also requires checking:
Forklift and crane capacity
Pallet rating
Filling equipment
Discharge equipment
Warehouse floor loading
Vehicle and container limits
Stacking assessment
Customer handling capability
A higher bag rating does not increase the capacity of the surrounding system.
Use the intended filling history as the starting point.
The bag will be filled once
The contents are non-dangerous
Refill after discharge is prohibited
The supply chain does not depend on returning empty bags
The approved design and test evidence match the application
Multiple fillings and discharges are deliberately planned
A controlled return or closed-loop system exists
The same type of contents will be carried during reuse
Each bag can be traced and inspected
Damaged bags can be removed from service
Cleaning will not damage the construction
The economics justify return, inspection, storage, and administration
The supplier provides evidence for the standard-duty reusable design
Do not choose 6:1 solely because:
The product is heavy
The route is long
The bag will be lifted many times during one filling cycle
A customer requests “extra strong bags” without defining the risk
The contents are dangerous
The warehouse wants a higher stack
Operators sometimes overload bags
Those conditions require their own technical review.
When comparing FIBC manufacturers, buyers should confirm that the stated SWL and safety factor are connected to an identifiable bag design rather than appearing only in a quotation or catalog table.
Request:
The approved drawing and revision.
The exact SWL.
The safety factor and FIBC class.
The intended single-trip or reusable service.
The applicable test standard and edition.
The cyclic top-lift test report.
The compression or stacking test evidence.
The test sample construction.
The filling material and filling height used during testing.
The manufacturing site covered by the evidence.
The permitted design range.
The final label artwork.
The controls used to prevent unapproved material or construction changes.
Routine inspection and traceability records.
Reuse and rejection instructions for 6:1 or 8:1 designs.
Separate evidence for dangerous-goods, electrostatic, food-contact, or other special requirements.
A test report should identify the bag it covers. A certificate showing only “1,000 kg, 5:1” is insufficient if it cannot be connected to the dimensions, loops, seams, fabric, production site, and finished marking of the ordered product.
Misinterpretation | Correct position |
|---|---|
“A 1,000 kg 5:1 bag can carry 5,000 kg.” | Its maximum service load remains 1,000 kg. |
“The extra test margin covers filling variation.” | The filling process must remain within SWL. |
“A 6:1 bag is simply a stronger one-way bag.” | Under ISO 21898, it represents a standard-duty reusable class. |
“A 6:1 bag can be reused until visible failure.” | Reuse requires controlled inspection and withdrawal before unsafe deterioration. |
“All reusable bags can be repaired.” | A damaged standard-duty reusable bag is not repairable under the category. |
“Replacing the liner makes a 5:1 bag reusable.” | A single-trip FIBC remains limited to one filling. |
“A 6:1 bag is automatically UN certified.” | UN approval requires the complete dangerous-goods design-type system and marking. |
“Safety factor determines stack height.” | Stacking capability is tested and marked separately. |
“Safety factor identifies Type C or Type D performance.” | Electrostatic classification is a separate requirement. |
“Higher GSM guarantees a higher safety factor.” | The complete bag system must pass the required tests. |
“A higher SF allows fewer lifting loops to be used.” | The bag must be lifted through the approved lifting configuration. |
“If there is no visible damage, the bag remains safe.” | Damage, ageing, and strength loss can exist without an obvious rupture. |
Before filling or lifting an FIBC:
Read the physical bag label.
Confirm the SWL against the planned payload.
Confirm whether the bag is single-trip or reusable.
Verify the intended contents.
Check that the filling process cannot exceed SWL.
Inspect the fabric, seams, loops, reinforcement, closures, and label.
Confirm that all required lifting devices will be used.
Check forklift tines and other handling equipment.
Keep personnel away from suspended loads.
Follow the separately marked stacking limit.
Do not use SF as an overload allowance.
Do not refill a 5:1 single-trip bag.
Do not reuse a damaged 6:1 standard-duty bag.
Verify separate UN or electrostatic requirements where applicable.
Safe Working Load and Safety Factor should always be read together, but they must never be multiplied to create a new operating capacity.
SWL is the maximum load the FIBC may carry in service. Under ISO 21898:2024, a 5:1 rating identifies a single-trip FIBC intended for one filling, while a 6:1 rating identifies a standard-duty reusable FIBC intended for a controlled, limited number of fillings and discharges. In both cases, the payload must remain within the marked SWL.
The safety factor does not determine permitted stacking, electrostatic classification, product compatibility, or dangerous-goods approval. Those requirements must be specified and verified separately.
Jebic Packaging can review the product, bulk density, target fill weight, handling method, reuse plan, operating environment, and applicable compliance requirements before confirming the appropriate SWL, safety factor, construction, marking, and test evidence for a new FIBC project.
SWL means Safe Working Load. It is the maximum load that the certified FIBC may carry during normal service. A bag marked SWL 1,000 kg must not contain more than 1,000 kg of product.
No. Five times SWL is associated with the final cyclic top-lift test load for the single-trip classification. It is not an authorized service payload. The marked SWL remains the maximum permitted load.
No. Under ISO 21898:2024, a 5:1 FIBC is a single-trip bag designed for one filling only. It must not be emptied and refilled, even if it appears undamaged.
ISO 21898 does not assign one universal trip count to every 6:1 bag. The number of uses must be controlled according to the approved design, contents, operating conditions, inspection results, supplier instructions, and reuse program.
A standard-duty reusable FIBC should not be reused if damaged and is not structurally repairable under that category. Replacing a removable liner is not considered a repair, but it does not restore damaged load-bearing components.
No. A 6:1 commercial rating alone does not establish UN approval. Dangerous-goods FIBCs require the correct design type, test program, UN marking, packing-group suitability, production controls, and regulatory documentation.
Only if it has a higher marked SWL. A 1,000 kg 5:1 bag and a 1,000 kg 6:1 bag both have a maximum service payload of 1,000 kg.
No. Permitted stacking is assessed and marked separately. A 6:1 rating does not mean six bags can be stacked.
No. Fabric GSM is only one design variable. Safety-factor performance depends on the complete FIBC, including fabric properties, loops, seams, thread, reinforcement, dimensions, construction, and production consistency.
No. A 5:1 design is appropriate for a properly controlled single-trip application. A 6:1 design is justified when planned reuse, inspection, traceability, and return logistics are genuinely required.
