The bag fabric is only half the containment story. The woven polypropylene face of any FIBC breathes, which is exactly what you want for sand and exactly what you do not want for a hygroscopic powder or a food ingredient. Liners close that gap, and choosing the wrong liner type costs more in rejected loads than the liner ever saved. We fit liners into bulk bags every production day, so here is the practical rundown we give US buyers.
The three liner families
Tubular liners are a straight polyethylene tube inserted into the bag and cut to length. They are the economical workhorse, typically adding $2.50 to $4.00 per bag, and they suit granules and pellets where the liner does not need to follow every bag corner. Folds of excess material settle at the bottom during filling, which is harmless for flowable product.
Form-fit liners are manufactured on the bag geometry itself, with gussets and corners matched to the panels. They seat cleanly during filling, present a smooth face to the discharge spout, and leave no loose film to restrict flow at the outlet. Food processors and fine-powder buyers overwhelmingly land here; expect $4.00 to $6.50 per bag depending on thickness and resin.
Barrier liners bring aluminum foil or EVOH co-extruded film into the structure for moisture- and oxygen-sensitive product. If you ship hygroscopic additives, certain vitamins or specialty chemicals across a humid ocean route into a Gulf Coast summer, this is the tier that protects you. Barrier adds the most cost and lead time, so we quote it case by case.
Food-grade is a resin and process claim, not a label
A food-contact liner should be made from virgin polyethylene compliant with FDA 21 CFR 177.1520 for olefin polymers, produced on lines with documented food-safety handling, and supplied with a certificate of analysis per lot. Ask your supplier to state the regulation on paper. If the answer is "food grade, trust us," keep walking. We also see buyers confuse food-contact compliance with sifting-proof seams; they are separate problems, and the liner solves the second one only when the fill and discharge spout cuffs are tied and closed correctly.
Fitments and static: the details buyers forget
Tell your liner supplier how the bag gets filled and emptied. A liner for a spout-top bag needs a tied-in fill cuff; a liner for an open-top duffle is a simpler cut. For discharge, the liner should extend into the outlet spout and petal-close with it, otherwise product bridges between liner and fabric. For flammable or combustible powders, static matters: ground the bag and discuss Type C conductive or Type D static-protective construction with the factory before ordering, because liner choice changes the grounding path.
Indicative cost picture
As liners ship inside the bag, freight impact is small but real: a lined container carries fewer bags per load. Budget roughly $2.50 to $4.00 for tubular, $4.00 to $6.50 for form-fit, and quote-based pricing for foil barrier, always FOB India before freight and duty. Production timelines stay at 3 to 4 weeks when the liner is specified with the bag; retrofitting a liner spec mid-order is what causes delays, not liner manufacturing itself.
Quick answers
Do I need a liner for pellets?
Usually not, unless moisture pickup or cross-contamination between product runs is a concern. Many resin distributors run uncoated, unlined bags successfully.
What thickness should a form-fit liner be?
2 to 3 mil suits most powders; 4 to 5 mil where product is abrasive or the bag gets handled roughly. We recommend thickness by product, not by habit.
Liner options, materials and fitment combinations are listed on our FIBC Liners page. Pair it with the right body construction from our U-panel vs circular guide, and check the price guide for how a liner changes landed cost.
