How to Choose an FIBC Liner

Choose the FIBC liner from what the product does inside the bag, not from what the bag looks like from outside. Start with five answers: is the product moisture sensitive, does it dust, does it contain oil or fat, what temperature is it when filled, and does it have to arrive dry after a long sea leg. Those answers set the film type, the thickness, the fit and the closure. A dry mineral powder that is not moisture sensitive often needs no liner at all, while a hygroscopic food powder moving through a humid port usually needs a sealed liner that acts as the moisture barrier. The liner is the part of the FIBC that most often decides whether a load arrives in specification.

Match the film to the product

Low-density polyethylene film at 50 to 80 micron is the usual starting point for dry, free-flowing powders and granules that only need dust containment. Hygroscopic products, fine flours and starches move up to 100 to 150 micron, and the specification usually includes a barrier requirement rather than a thickness alone. Products with oil or fat content need a film checked for compatibility, because some fats soften or swell the film over a long sea leg. Warm-fill products are a separate case: the film and the seal have to be specified for the fill temperature, and a liner that seals cleanly at ambient temperature can fail on a warm product.

Fit decides how the liner behaves on your line

• A loose liner is fastest to fit and cheapest, and is fine when the product is coarse and the bag is filled slowly.
• A tubular or form-fit liner is tied or welded to the bag so it stays open during filling and does not fold into the product stream.
• A baffle liner is used when the filled bag has to hold a square footprint on a pallet; it costs more and slows filling slightly.
• An inlet spout on the liner, rather than an open top, keeps the product stream enclosed and reduces dust at the fill head.

Thickness is a range, not a guarantee

Film thickness is specified as a nominal figure and measured on a sample. A nominal 100 micron film can run a few micron either side of the target, and where a barrier property matters the seal is the weak point rather than the film body. This is why the useful questions are about seal type and seal width, not only micron: a 120 mm wide seal on a 100 micron film behaves very differently from a narrow seal on the same film.

QINFENG’s first-hand experience

The liner problems we see are almost never the film body. They are the seal and the fit. A liner that is slightly too tall folds over at the fill head, powder collects in the fold, and the seal is contaminated before it is closed. A liner that is slightly too short pulls out of the bag during discharge and tears at the spout. Both are drawing errors rather than material errors, so our liner drawings now carry the filled height and the fill-head clearance, and each food-contact batch keeps a retained sample with its seal check. When a customer reports a moisture excursion, the first thing we ask for is the bag serial, which links back to the film roll and the shift that packed it.

Where the liner cannot help you

A liner controls moisture and dust ingress through the bag; it does not control the humidity inside a container, the condition of the receiving warehouse, or what happens after the liner is opened. It also does not make a bag suitable for food contact on its own, and it does not replace a written direct-contact specification where your market has one. If the product is a fine powder in a humid corridor, a liner alone may not hold the required moisture level, and the answer is usually a combination of liner specification, desiccant and a shorter transit window. Third-party testing is arranged on request and quoted separately.