Under ISO 21898:2024, the international standard governing FIBCs for non-dangerous goods, every bulk bag must carry a durable label that remains readable after the bag is filled. The label must include the following:
The manufacturer’s name and address, or a registered symbol identifying the manufacturer. This is the accountability anchor of the label; if something goes wrong with the bag, this is where the trail starts.
The type test certificate number, which is unique to the bag design. This number links the bag to its certification documentation. If your operation requires proof of compliance, this is the number you quote when requesting test reports from the supplier.
The month and year of manufacture, expressed in numerals. This matters for two reasons: polypropylene degrades under UV exposure over time, and some certifications have validity windows. A bag manufactured years before use in a high-UV environment or under a certification with an expiry date may not be fit for purpose even if it looks fine.
The safe working load (SWL) in kilograms. The maximum weight the bag is designed and tested to carry under normal operating conditions. This is the number most operators know, but it is also the one most often exceeded when product density is not calculated accurately.
The safety factor (SF) is expressed as a ratio, either 5:1 or 6:1. This tells you the relationship between the bag’s rated capacity and the load at which it was tested to fail. A 5:1 bag with a 1,000 kg SWL was tested to withstand 5,000 kg before failure. A 6:1 bag is stronger, required for multi-trip use and for UN-certified applications.
The maximum stacking load is a requirement added by the updated ISO 21898:2024 standard. This specifies the maximum compressive load the bag can withstand when other filled bags are stacked on top of it. Storage operations that stack two or three bags high need this number, not just the SWL.
The filling and emptying instructions vary by bag design and discharge configuration. These are particularly relevant for bags with discharge spouts, baffles, or specific orientation requirements.
Where the bag is certified for a specific product, the product description must appear on the label. This matters when a bag has been type-tested with a particular material; reusing it for a different product may invalidate the certification.
These two numbers appear on every FIBC label and are the most practically important and the most commonly misread.
The SWL is the ceiling, not a suggestion. Loading a bag beyond its SWL compresses the safety margin built into the design and, beyond a certain point, risks structural failure. The SF is what that margin looks like in tested numbers: a 5:1 bag at 1,000 kg SWL was confirmed to hold 5,000 kg in controlled testing before the fabric, seams, or loops gave way. That gap exists to cover handling dynamics, swinging loads, forklift tines pressing on fabric, vibration during transport, not to provide extra carrying capacity.
The distinction between 5:1 and 6:1 is also a signal about intended use. A 5:1 safety factor means the bag is designed for a single fill-and-empty cycle. A 6:1 safety factor means the bag was tested more rigorously, specifically through 70 cyclic top-lift cycles at three times the SWL before the final load-to-failure test, and can be reused across multiple cycles, provided it passes inspection between uses.
If you are procuring bags and the SF is not on the label, that is a red flag. For more details on how these safety margins are calculated and what the tests involve, the FIBC safety factors guide covers the full methodology.
Standard FIBC labels and UN markings are two separate things. A bag can carry an ISO-compliant standard label without any UN marking. A UN marking only appears on bags that have been certified for the transport of dangerous goods through accredited third-party testing.
The UN marking follows a standard format: 13H3/Y/250/S/19/D/ABC123
Each element of this string has a specific meaning:
13 identifies the container as a flexible intermediate bulk container, the designation within the UN packaging classification system.
H indicates the material. H designates woven plastic fabric (polypropylene or polyethylene). Other letters appear for different materials, but H is by far the most common on standard FIBCs.
3 is the design type code within the flexible container category. The number identifies the construction configuration, whether the bag has a liner, how the fill and discharge are configured, and other structural details.
Y is the packing group designation. Dangerous goods are classified into three packing groups: X for great danger (Packing Group I), Y for medium danger (Packing Group II), and Z for low danger (Packing Group III). A Y marking means the bag is certified for materials in Packing Groups II and III, covering the majority of industrial chemicals and hazardous powders most operations encounter.
250 is the maximum gross mass in kilograms the bag is certified to carry.
S indicates the bag passed the drop test in the solid/granular condition, relevant for dry bulk materials. An alternative code indicates liquid testing, though liquid-carrying FIBCs are less common.
19 is the two-digit year of manufacture.
D is the country code for the country that authorised the certification. D indicates Germany; US indicates the United States; and so on.
ABC123 is the manufacturer’s identifier or approval code, linking the marking back to the certified manufacturer.
For a full breakdown of the UN marking system, including packing group classifications and what hazard classes each covers, the UN markings for FIBCs guide covers the complete decoding process. For operations that actually need UN-certified bags, the UN-certified vs standard FIBC comparison explains when certification is required and when it is not.
FIBC labels on bags manufactured for environments where static discharge is a risk will carry a type designation: A, B, C, or D. This marking is not part of the standard ISO 21898 label requirement for all bags, it only appears when the bag has been designed and tested to a specific electrostatic performance level under IEC 61340-4-4.
Type A bags are standard woven polypropylene with no static protection. They are safe for non-flammable products in environments where no flammable solvent vapors or combustible dusts are present.
Type B bags are manufactured from low-breakdown-voltage fabric that limits the energy of sparks generated by the bag surface. They are not anti-static; they provide no path for charge dissipation, but the spark energy is low enough to prevent ignition of most flammable vapors. They cannot be used where combustible dusts are present.
Type C bags contain a grid of conductive threads woven through the fabric. These threads must be connected to earth during filling and emptying to safely dissipate static charge. An ungrounded Type C bag provides no static protection and is more hazardous than a Type A bag because the conductive threads can concentrate charge rather than dissipate it. The grounding requirement must appear on the label.
Type D bags use static dissipative threads that discharge safely to the surrounding atmosphere without requiring grounding. They provide equivalent protection to a grounded Type C bag but remove the grounding dependency, which reduces handling complexity in operations where grounding cannot always be verified.
If your product is a combustible powder, flammable pellet, or handled in an environment with solvent vapors, the type designation on the label determines whether the bag is safe to use. For a detailed guide on which type fits which application, the different types of FIBC bags article covers the full decision framework.
ISO 21898 requires manufacturers to maintain documented material specifications and a statement of conformity for each production batch. The batch number on the label is the link between the physical bag and that documentation.
In practice, a batch number allows you to trace the bag back to the specific production run, the fabric weight used, the seam construction, the test date, and the quality control records. For regulated applications (food-grade, pharmaceutical, or UN-certified), the ability to present batch-level documentation is often a compliance requirement rather than an optional extra.
If a bag arrives without a legible batch number or manufacture date, that is a reason to pause before using it. Suppliers who manage production properly can pull traceability records by batch number. Those who cannot should raise questions about the reliability of their quality controls.
ISO 21898:2024 added a specific requirement that all certified FIBCs carry a maximum stacking capacity marking. Before this update, stacking guidance was handled in product documentation rather than on the label itself, which meant warehouse teams often stacked bags without a clear reference point.
The stacking load is not the same as the SWL. A bag with a 1,000 kg SWL may have a stacking load of 2,000 kg, meaning it can safely bear two similar filled bags on top of it, or it may have a lower stacking limit depending on the bag’s base dimensions and structural design. Exceeding the stacking load compresses the lower bag’s fabric and seams over time, and in warehouse environments where bags sit stacked for weeks, this is a failure mode that builds slowly rather than appearing immediately.
For operations that routinely stack three bags high, checking the stacking load on the label is worth adding to the goods-in procedure.
What is the difference between SWL and SF on an FIBC label? SWL (Safe Working Load) is the maximum weight the bag is designed to carry. SF (Safety Factor) is the ratio of the tested failure load to the SWL. A 5:1 SF on a 1,000 kg SWL bag means it was tested to 5,000 kg before failure. The SF is a safety margin, not additional carrying capacity.
Does every FIBC need a UN marking? No. UN markings only appear on bags certified for the transport of dangerous goods under UN regulations. Standard FIBCs for non-hazardous materials carry an ISO 21898 label without UN marking.
What does the Y in a UN marking mean? Y indicates the bag is certified for Packing Group II and III dangerous goods, medium and low danger classifications. X indicates Packing Group I (high danger). Z covers Packing Group III only.
Can I reuse a bag marked with a 5:1 safety factor? No. A 5:1 SF designation indicates a single-trip FIBC. Reuse is not permitted under ISO 21898. Multi-trip use requires a 6:1 SF bag, which has been tested through 70 cyclic load cycles before the final failure test.
What should I do if a bag label is missing or unreadable? Do not use the bag. An unreadable or missing label means the bag’s SWL, SF, certification status, and manufacture date cannot be verified. Contact the supplier and request a replacement with full labeling or supporting documentation.
What is the Type C grounding requirement on an FIBC label? Type C bags contain conductive threads that must be connected to earth ground during filling and emptying. The grounding requirement must be printed on the label. Using a Type C bag without grounding can concentrate static charge rather than dissipate it, creating a higher ignition risk than using no static protection at all.
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