How FIBC bulk bags are made
An FIBC starts as polypropylene granules mixed with a UV stabiliser and often a filler. The mix is extruded into film, slit into tapes and stretched, and the tapes are woven on circular or flat looms into tubular or flat fabric. Fabric may be coated with a thin polypropylene layer to stop fine powder leaking. It is then cut, printed and sewn: body panels, top and bottom, filling and discharge spouts, and four lifting loops, which carry the whole load.
Polyethylene liners keep out moisture, baffles keep a square shape, and sift-proof seams with a filler cord stop powder escaping through needle holes. Conductive threads make a Type C bag; special fabrics make Type B or Type D bags. Food and pharmaceutical bags are sewn in clean conditions and passed over light tables to find loose threads and contamination.
India exported US$1,074.5 million of FIBCs (HS 630532) in FY2025-26, according to Department of Commerce TradeStat; the figure is provisional. We have not found an official source naming FIBC clusters, so we name no town.
What we check on FIBC bulk bags
| Check | How it is checked | What fails |
|---|---|---|
| Dimensions | Body width, length and height, spout diameters and lengths, loop height measured against the drawing | Body or spout outside tolerance; loops too short for the buyer's forklift or hooks |
| Fabric | Fabric GSM from the factory's roll records and a weighed swatch from spare fabric of the same lot; coating checked | Fabric lighter than the type-tested design; uncoated where coated was ordered |
| Loops and seams | Stitch count per inch, thread, stitch pattern at loop attachments, seam type and sift-proofing | Skipped or loose stitches at loops; seam construction different from the tested design |
| Liner and closures | Liner fit, thickness and attachment; spout ties and closures | Missing or torn liner; liner not fixed where specified |
| Label and print | Safe working load, safety factor, standard, electrostatic type, maker and date read on every sampled bag; print checked against the artwork | Wrong SWL or safety factor; type marked that the bag is not |
| Cleanliness | Food and pharma bags opened over a light table; loose threads, insects, dust and foreign material looked for | Any contamination inside a food-grade bag |
| Electrostatic type | Type C: earthing tabs and conductive threads present and connected as drawn; Type B and D: fabric and test report checked | Earthing tab missing; type report for another fabric |
| Top-lift test | Bags chosen at random by the inspector; factory's own test run and witnessed; load, result and rig calibration date recorded | Loop or seam failure below the required load |
Top-lift tests, safety factors and our role
ISO 21898 covers FIBCs for non-dangerous goods. Each bag carries a safe working load (SWL), the rated filled weight, and a safety factor (SF): the ratio of the load the design must withstand in testing to its SWL. The standard uses 5:1 for single-trip bags and 6:1 for multi-trip bags. Type tests include top-lift tests, in which a filled bag is lifted by its loops, and the design must withstand its SF times its SWL. A 1,000 kg single-trip bag therefore has to withstand 5,000 kg on its loops in the type test.
Clear To Load does not own a test rig or a lab. We do three things instead. We check that the type-test report covers the exact design shipped: fabric weight, loop type, body size and SWL. We pick bags at random from the lot and witness the factory's routine top-lift test on its own rig, recording the load reached and how the bag behaved. And we pull and seal fabric or bags for an accredited lab where the buyer wants independent results, through lab testing coordination. Our report states what we witnessed and does not present it as a type test.
Common defects in FIBC bulk bags
| Defect | Why it matters | Class |
|---|---|---|
| Loop or seam fails in the witnessed test | Bags can fail while lifted over people | Critical |
| SWL, SF or type on the label not supported by a test report | The user relies on the label to lift safely and to avoid static ignition | Critical |
| Type C bag without connected earthing tab | Cannot be earthed during filling of flammable powders | Critical |
| UN mark without a matching design approval | Dangerous goods shipped in unapproved packaging | Critical |
| Foreign matter inside a food-grade bag | Contaminates food or pharmaceutical product | Critical |
| Skipped stitches at loop attachments | Weakens the load path | Major |
| Fabric lighter than the tested design | Safety margin smaller than the label claims | Major |
| Dimensions or spouts outside tolerance | Bag will not fit the filling or discharge station | Major |
| Seams not sift-proof where ordered | Powder leaks in transit | Major |
| Print smudges, loose external threads | Appearance only | Minor |
Standards and rules for bulk bags
- ISO 21898. Design, type testing and marking of FIBCs for non-dangerous solids. Buyers usually make it a contract term.
- IEC 61340-4-4. Classifies bags by electrostatic behaviour. Type A has no protection and is for non-flammable products away from flammable atmospheres. Type B uses fabric with a low breakdown voltage. Type C has interconnected conductive threads and must be earthed during filling and emptying. Type D uses static-dissipative fabric and is used without earthing. The type must match the product and the place of use.
- UN 13H bags for dangerous goods. Woven plastic flexible IBCs carrying dangerous goods must be of a design that passed the tests in the UN Model Regulations, as carried into ADR for road and the IMDG Code for sea, and must carry the UN mark with their code, the packing groups allowed and the approval details.
- Food contact. Bags and liners for food must be made of compliant plastics: Regulation (EU) No 10/2011 in the EU, and FDA 21 CFR 177.1520 for polyolefins in the US. See EU food contact rules and FDA food contact. Many buyers also require BRCGS Packaging certification of the plant.
Packing, transit and your purchase order
Bags are folded flat, stacked and pressed into bales, then strapped and wrapped, or palletised. Food-grade bags are packed in sealed outer covers so they stay clean. Polypropylene loses strength in sunlight, so bales should not wait outdoors. The inspector counts bales and bags per bale against the packing list and checks that bales and container are dry and clean.
Put these in your purchase order:
- Drawing with body size, top and bottom design, spouts, loop type and height, and tolerances.
- SWL, safety factor, single or multi-trip, and the type-test report for that design.
- Fabric GSM, coating, colour and UV stabilisation.
- Seam type, stitch count, sift-proofing, liner and baffles.
- Electrostatic type, with its test report; for dangerous goods, the UN code and approval.
- Food grade requirements, clean-room conditions and certificates.
- Label and print artwork; bales, bag count per bale and pallet pattern.
- How many bags are to be top-lift tested in your presence, and to what load.
A factory audit before the first order shows whether the test rig, light tables and batch records exist as described. Book an inspection anywhere in India.
Sources
- Department of Commerce, TradeStat: commodity-wise exports (HS 630532, FY2025-26 provisional)
- ISO 21898:2024, Packaging: Flexible intermediate bulk containers (FIBCs) for non-dangerous goods
- BSI: IEC 61340-4-4, Electrostatic classification of flexible intermediate bulk containers
- UNECE: Transport of dangerous goods (UN Model Regulations, ADR)
- Commission Regulation (EU) No 10/2011 on plastic materials in contact with food (EUR-Lex)
- 21 CFR 177.1520, Olefin polymers (eCFR)