How to Read FIBC Bag Specs: SWL, Safety Factor & Liners

An FIBC bag spec sheet is full of abbreviations that look intimidating at first, but the logic behind them is straightforward once you break it down. Here are the four things worth understanding before you order: load rating, safety factor, dimensions, and whether you need a liner.

SWL: What It Actually Means

SWL (Safe Working Load) is the single most important number on an FIBC spec sheet. It's the maximum load the bag is designed to carry under normal, repeated use — not the bag's absolute breaking point. An SWL of 1,000 kg means the bag is engineered to safely carry 1,000 kg load after load, with margin built in from the start.

Safety Factor: Where the Real Limit Is

The bag's actual breaking strength is a multiple of its SWL — that multiple is the safety factor. A common industry standard for general industrial use is 5:1, meaning a bag rated for 1,000 kg SWL should test to at least 5,000 kg before failure. Applications closer to food or pharmaceutical use typically call for a stricter safety factor. It's reasonable to ask your supplier directly what safety factor a given bag is built to — it's one of the clearest signals of how solidly a bag is actually constructed.

Reading the Dimensions

FIBC dimensions are usually given as length × width × height, in centimeters. Length and width determine the footprint once filled; height matters for warehouse ceiling clearance and how the bag stacks in a container. Two bags rated for the same 1,000 kg load can have very different proportions — a taller, narrower bag versus a shorter, wider one changes both stacking pattern and container loading efficiency. It's worth checking your warehouse and shipping constraints before locking in a size.

Do You Need a Liner?

A liner is a plastic film insert on the inside of the bag, mainly there to block moisture, dust, and fine powder from working through the woven fabric. If you're shipping something like dry mortar or sand — or a moisture-sensitive material like grain or plastic pellets — a liner is generally worth it. If your material is coarser and doesn't mind some humidity, skipping the liner keeps cost down. Liners also come in sewn-in versus separate-insert styles, which trade off moisture protection against cost — worth discussing with your supplier for your specific case.

PackKing's Standard Specs at a Glance

If you'd rather not work out specs from scratch, PackKing™ offers 5 standard stock sizes, all rated at 1,000 kg SWL, ranging from 90×90×100cm to 95×95×170cm.