FIBC Bulk Bags,
Explained Properly
A working reference for sizing, safe working loads, lift-loop types, coatings, and UN certification codes — written for buyers who need to spec a bag correctly the first time, not marketing copy.
What an FIBC actually is
A Flexible Intermediate Bulk Container (FIBC) — also called a bulk bag, super sack, or tote bag — is a woven polypropylene container built to move and store dry, flowable products in quantities between roughly 1,000 and 4,400 lbs. The fabric is engineered, not just sewn: fill weight, stacking height, lift method, and the product's static properties all determine which construction is correct.
- ALift loops — top corner or cross-corner loops rated to the bag's Safe Working Load; loop count and orientation determine lift method (single-point vs. 4-point forklift/crane).
- BFill spout — top opening for gravity or pneumatic filling; can be duffle-top, spout-top, or open-top with flap.
- CBody panel — woven polypropylene fabric, typically 5–6.5 oz/yd²; baffled construction squares off the bag for denser palletizing.
- DBaffles — internal fabric panels sewn corner-to-corner that let the bag hold a stable cube shape under load instead of bulging.
- EDischarge spout — bottom outlet for controlled emptying; secured with a tie, clip, or spout closure strap.
The four FIBC types
Standard, non-conductive
Plain woven polypropylene with no static protection. Fine for non-flammable, non-combustible products in areas without flammable atmospheres. Lowest cost option.
Low breakdown-voltage
Fabric engineered to keep breakdown voltage under 6kV, preventing propagating brush discharge. Used around combustible dusts where a Type A bag would be a hazard.
Conductive / groundable
Woven with conductive threads in a grid, forming a Faraday cage. Must be grounded via a clip during fill and discharge — required around flammable solvents and dusts.
Static-dissipative
Dissipates static without a ground connection, using engineered fabric rather than conductive threads. Common where grounding a Type C bag isn't practical.
Standard sizing reference
Bag footprint is typically matched to a 48"×40" pallet. The table below covers the most-ordered configurations; custom cube and fill-weight combinations are available on request.
| Footprint | Height | Fill Weight (SWL) | Volume | Typical Use |
|---|---|---|---|---|
| 35" × 35" | 35" | 1,000–1,500 lbs | ~30 ft³ | Resins, powders, small aggregate |
| 36" × 36" | 36"–45" | 1,500–2,200 lbs | ~35–45 ft³ | General dry bulk, minerals |
| 39" × 39" | 39"–47" | 2,000–2,500 lbs | ~45–52 ft³ | Sand, gravel, feed, seed |
| 41" × 41" | 44"–53" | 2,500–3,000 lbs | ~52–58 ft³ | Construction aggregate |
| 45" × 45" | 45"–54" | 3,000–4,000 lbs | ~58–65 ft³ | High-density minerals, ore |
| 48" × 48" | 48"–60" | 3,500–4,400 lbs | ~65–75 ft³ | Max-cube bulk shipments |
Safe Working Load & safety factor
Safe Working Load (SWL) is the maximum fill weight a bag is rated to carry — not the weight it will fail at. Every FIBC is built with a Safety Factor (SF), a multiplier between SWL and actual break strength, set by the bag's application:
A 5:1 bag rated for a 2,000 lb SWL is tested to withstand 10,000 lbs before failure. Never exceed the stamped SWL, and never assume a bag is multi-trip rated unless it's explicitly marked — reusing a single-trip bag is a common and preventable failure point.
Reading a UN certification code
If you're shipping a hazardous material (per 49 CFR / IMDG / ADR), the FIBC must carry a UN code. It looks like 13H4/Y/0824/USA/1234 — here's how to decode it:
Container class — 13 is flexible bulk container.
Material — H is woven plastic (most common FIBC fabric).
Sub-type — governs liner and body construction, e.g. 4 = with liner.
Packing Group — X (most stringent) through Z (least).
Month/year of manufacture — certs are valid for a defined service window.
Common questions
Can I reuse a single-trip FIBC?
No, unless it's explicitly rated for multi-trip use (6:1 safety factor). Single-trip bags (5:1) are certified for one fill/transport/discharge cycle only — reuse voids the rating.
Do I need a liner?
Woven poly is not moisture- or dust-tight on its own. Liners (loose PE, form-fit, or laminated) are needed for hygroscopic products, fine powders, or moisture-sensitive materials.
How many lift loops do I need?
4-loop bags are standard for forklift or crane lifting with a spreader bar. 1-loop and 2-loop bags exist for specific single-point or crane-hook applications but require different SWL engineering.
What's the difference between a duffle top and a spout top?
A duffle top is a full-width fabric extension gathered and tied shut — faster to fill, harder to seal fully dust-tight. A spout top is a narrower sleeve better suited to controlled or automated filling lines.
Not sure which FIBC spec fits your product?
Tell us your fill weight, product density, and handling method — we'll spec the right bag and quote it same day.