FIBC Safety Factor 5:1 vs 6:1: Single vs Multi-Trip Bags
FIBC Safety Factor: 5:1 vs 6:1 Explained
Every FIBC bulk bag carries a safety factor, printed on its label as a ratio: usually 5:1 or 6:1. A 5:1 bag is designed for a single trip, and a 6:1 bag is designed to be cleaned, inspected and used again. The ratio is not a margin you are allowed to fill into. Treating it as spare capacity, or reusing a single-trip bag, are two of the most common causes of bulk bag failure.
This guide explains what the ratio means, how it is tested, when each rating is the right choice, and what a safe reuse programme actually requires.
What the safety factor means
The Safe Working Load (SWL) is the maximum weight of product the bag is rated to carry. The safety factor is the ratio between the load the bag must survive in testing and that SWL.
Rating | SWL | Must withstand in testing |
|---|---|---|
5:1 | 1,000 kg | 5,000 kg |
6:1 | 1,000 kg | 6,000 kg |
5:1 | 1,500 kg | 7,500 kg |
6:1 | 1,500 kg | 9,000 kg |
The reserve exists because real handling is far harsher than a static load. A bag swinging on a crane hook, a forklift braking, a bag dropped a few centimetres onto a pallet, a loop snagging: each of these briefly multiplies the force on the fabric and loops well beyond the product's weight. The safety factor covers those moments. It is not extra capacity. A 1,000 kg SWL bag must never be filled with more than 1,000 kg, whatever its ratio.
How the rating is tested
FIBCs for non-dangerous goods are tested under the international standard ISO 21898. The test that sets the safety factor is the top-lift test: the bag is filled, then lifted by its loops through repeated loading cycles, and finally loaded until it reaches the required multiple of its SWL.
To earn 5:1, the bag must survive the cyclic test and then withstand five times its SWL.
To earn 6:1, the bag must meet a more demanding cyclic test and then withstand six times its SWL.
The extra cycles matter more than the extra multiple. A multi-trip bag isn't only stronger on day one. It is built to keep its strength after repeated filling, lifting and emptying.
Bags for dangerous goods are tested under a separate UN regime and carry UN markings. That is a different certification, not a higher safety factor.
Why 6:1 is not just "20% stronger"
The numbers suggest a small difference: 6 against 5. In practice the two are built for different lives.
A single-trip bag is designed to be filled, moved, emptied and retired. Every component is specified for that one journey.
A multi-trip bag expects many journeys. Fabric, loops and stitching are specified to resist the fatigue that builds up with every cycle. Woven polypropylene loses strength with repeated stress, abrasion and exposure to sunlight. A multi-trip bag is built so that after many trips it still holds its rating.
That is why reusing a 5:1 bag is dangerous even when it looks undamaged. It was never designed to have strength left for a second trip. Visible damage often appears only at the moment of failure.
When to choose 5:1
A 5:1 single-trip bag is the right choice when:
The bag leaves your control. Export shipments are the clearest example: the bag goes to the customer and you cannot inspect it again.
The product contaminates the bag. Sticky, abrasive or reactive contents that cannot be fully cleaned out.
Food or pharma hygiene rules require single use. Many buyers in these sectors specify single-trip bags to remove any cross-contamination risk.
You have no reuse system. Without cleaning, inspection and trip tracking, a reusable bag gives you the cost of a 6:1 bag and the risk of a 5:1 one.
For most one-way shipments, 5:1 is the correct and economical specification.
When to choose 6:1
A 6:1 multi-trip bag makes sense when:
The bags come back to you. Closed-loop systems between your plant and a known customer, a warehouse, or between your own sites.
The product is clean and dry. Free-flowing granules and powders that empty completely and leave little residue.
You can run a reuse programme. Cleaning, inspection before every fill, and records of how many trips each bag has made.
The bag costs more to buy. Whether it is cheaper per trip depends on how many trips each bag actually completes and what the cleaning and inspection cost you. That arithmetic is worth doing before you switch.
What a safe reuse programme requires
A 6:1 rating makes reuse possible; your process makes it safe. The essentials:
Clean and empty. Remove all residue, and make sure no previous product can contaminate the next fill.
Inspect before every fill. Check the loops, loop stitching, body seams and fabric for cuts, abrasion, fraying, burns or brittleness.
Check for sunlight damage. Polypropylene degrades under UV light. Bags left outdoors lose strength even when unused, and faded, chalky or stiff fabric is a reason to retire a bag.
Track the trips. Know how many times each bag has been used, and retire it at the limit your supplier recommends.
Never repair loops. A damaged loop means the bag is retired.
Keep the product the same. Reuse for the same or a compatible product, so contamination isn't introduced.
Store properly. Indoors, dry, away from sunlight, and off the floor.
If any step is impractical at your site, single-trip bags are the safer choice.
Reading the label
Every FIBC should carry a label sewn into the body. At minimum, check:
SWL in kilograms
Safety factor: 5:1 or 6:1
Manufacturer and production date or batch
The standard it was tested to
Static type (A, B, C or D), if relevant
Handling instructions
If a bag has no label, or the label is unreadable, do not lift it. You have no way of knowing what it was built for.
Common mistakes
Filling to the safety factor. "It's rated 5:1, so 1,200 kg in a 1,000 kg bag is fine." It isn't. The reserve is for handling forces, not product.
Reusing a 5:1 bag "just once more". A single-trip bag has no designed strength for a second trip.
Buying 6:1 without a reuse system. The rating alone does not make reuse safe.
Leaving bags in the sun. UV damage is invisible at first and progressive, so outdoor storage shortens the life of every bag.
Lifting by fewer loops than designed. Taking a four-loop bag on two loops doubles the load on each one.
Shish FIBC bags
Shish manufactures FIBC bulk bags in both 5:1 single-trip and 6:1 multi-trip ratings, with SWL from 500 to 2,000 kg, in U-panel, circular, baffle, conductive (Type C), food-clean and UN constructions. Production is BRCGS certified; see our full certifications. For the other choices behind a bag, including body type, loops, discharge and static protection, read our guide to FIBC bulk bag types and safe working load. Specifications are on the FIBC bulk bags page.
Frequently asked questions
What does 5:1 mean on an FIBC?
It means the bag has been tested to withstand five times its Safe Working Load. A 1,000 kg SWL bag at 5:1 is tested to 5,000 kg. It is designed for a single trip.
Can I put more than the SWL into a 6:1 bag?
No. The SWL is the maximum product weight for every bag, whatever its safety factor. The extra strength of a 6:1 bag is there so it survives repeated use, not so it can carry more.
How many times can a 6:1 FIBC be reused?
It depends on the product, handling conditions and how well the bag is cleaned, inspected and stored. Your supplier should give a recommended trip limit, and every bag should be inspected before each fill regardless.
Is a 6:1 bag better for export?
Usually not. If the bag goes to an overseas customer and will not come back to you, you cannot control its reuse, so a 5:1 single-trip bag is normally the correct and more economical choice.
Does a UN-certified bag have a higher safety factor?
UN certification is a separate qualification for transporting dangerous goods, with its own test regime. It is not the same thing as a 6:1 rating, and a bag can carry both, either or neither.
Why do FIBCs fail?
The most common causes are overfilling beyond SWL, reusing single-trip bags, damage to loops, UV degradation from outdoor storage, and lifting by fewer loops than the bag was designed for.
Get the right rating specified
Tell us your product, the weight per bag, and whether the bags come back to you. Our team will recommend 5:1 or 6:1, explain the reasoning, and quote against a specification you can check.
Request an FIBC specification and quote
Or speak to the team through the contact page.
