Coated fabric bulk bags
A coated bulk bag is woven polypropylene with a thin polypropylene layer laminated onto one face of the fabric, which closes the gaps in the weave. That keeps fine powder from sifting through the walls and slows moisture, though a coating alone is not a waterproof seal; a liner does that job.
| Fabric | Woven polypropylene with a polypropylene coating on one face |
|---|---|
| Coating side | Inside or outside, per the maker and the order |
| Purpose | Stops sifting and dusting through the weave |
| Seams | Standard, or sift-proof with filler cord sewn in |
| Top | Spout top or duffle top |
| Bottom | Discharge spout or flat |
| Loops | Four, corner or cross-corner |
| SWL | Commonly 2,000 to 3,000 lb |
| Static type | Type A unless ordered otherwise; coating does not set the type |
| Liner | Optional; add one when moisture really matters |
Good for
- Fine powders like cement, lime, talc or pigments
- Flour, sugar and starch on food lines, in new bags
- Fertilizer that cakes when it picks up humidity
- Mineral fillers and ground minerals
- Pigments, clays and kaolin
- Any load where dust on the trailer floor is a complaint
Not for
- Produce, firewood and anything that needs to breathe
- Moisture-critical products with no liner
- Coarse aggregate, where an uncoated bag is enough
- Hot product straight from a dryer, unless the maker confirms the fabric can take it
- Damp organic material that would sweat and turn mouldy behind a sealed weave
Put this in the request
- How fine is the product: will it sift through an uncoated weave?
- Is moisture a concern, will filled bags cross humid regions or sit through a wet season, and is a liner needed on top of the coating?
- Does residue have to be scraped or washed out of trailers today?
- Standard seams, or sift-proof seams with filler cord?
- What top and bottom, and what spout sizes?
- What static type does the product or area require?
- Is it a food line, which means new bags?
- What SWL and monthly quantity, and to which ZIP?
What the coating is, layer by layer
Woven fabric is made of flat polypropylene tapes crossed over and under each other. However tight the weave, there are tiny gaps where the tapes cross. Coarse product never notices them. Cement, talc or flour finds them, and an uncoated bag full of fine powder leaves a dusting on every surface it touches.
Coating is a thin film of molten polypropylene laid onto one face of the woven fabric so it bonds into the surface and seals those gaps. The fabric still carries the load; the coating keeps the product in. It is part of the cloth, unlike a liner, which is a separate film bag sitting inside.
Weight and color are the other choices in the cloth. Heavier fabric shrugs off more abuse at the forks; lighter fabric folds smaller in the bale. Natural white is usual, and some plants ask for a tinted fabric so their bags are easy to tell apart from a neighbour's on a shared dock.
Bare cloth has one quiet advantage: trapped air escapes through it while the bag fills, so the load settles faster. Coated bags can balloon a little on quick fillers, and some lines add deaeration probes or vibration tables to compensate.
Seams are the next weak point
Once the walls are sealed, powder heads for the needle holes along the seams. Sift-proof construction sews a filler cord or tape into each seam so the holes close up around it. For very fine product, ask for coated fabric and sift-proof seams together; one without the other still leaks.
The spouts matter as well. A loosely tied discharge spout will weep powder in transit. Ask for a spout closure that suits the product, and tie it the way the maker describes.
- Filler cord or tape in every seam
- Coated fabric on all panels, including top and floor
- Spouts tied snug and tucked under their cover flap
- A liner for powders that are both fine and moisture-sensitive
Coated or uncoated, and where liners come in
Uncoated fabric breathes. That's what you want for potatoes, onions, firewood or damp material that needs to dry, and it's adequate for gravel and many pellets. Coated fabric is for fines and for cutting down on moisture pickup in a dry warehouse.
Neither one is a moisture barrier. Humid air gets in through seams and the top closure, so a hygroscopic product shipped through a wet season needs a polyethylene or polypropylene liner. The coating keeps dust off the trailer; the liner keeps water out of the product.
Climate shifts the decision too. A Gulf Coast warehouse in August and a dry Rocky Mountain shed are very different places to keep a hygroscopic powder, and a bag that works fine in one may let product clump in the other.
| Need | What to ask for |
|---|---|
| Coarse product, no dust issue | Uncoated fabric |
| Fine powder | Coated fabric, sift-proof seams |
| Product must stay dry | Coated fabric plus a liner |
| Product must breathe | Uncoated or vented fabric |
On the pallet and on the trailer
Coated bags are a little stiffer than uncoated ones, but they still fold flat into strapped bales on wrapped pallets. If the order includes liners, say whether they should come installed or loose; installed liners ship ready to fill, loose ones save a little space on the pallet. A small order moves LTL, and repeat volume to one plant is usually cheaper per bag as a full truckload.
Empties headed back for buy-back or recycling should be shaken out and kept dry. Bags with product still caked in the seams are harder to place, and damp ones carrying organic residue can spoil inside the bale.
What belongs in the coated bag request
Name the product and how fine it is, the fill weight, the top and bottom, seams, liner or not, static type, and whether it's a food line. Add the ZIP and how many bags you run in a month. Coating is a fabric choice, so the static type and food grade questions still need their own answers, and we'll ask if they're missing.
Printed walls are another option many makers offer: a product name, a lot field or handling marks such as keep dry. Printing sits beside the maker's sewn label, never in place of it.
Questions
Does a coated bag keep rain out?
Partly. The walls shed water, but seams and the top closure don't. Store filled bags under cover, and add a liner if the product can't take any moisture.
Does coating make a bag Type B or Type D?
No. Static type comes from the fabric and yarns the maker uses and is marked on the label. A coated bag is Type A unless it is built and labeled as another type.
Is the coating inside or outside?
Either, depending on the maker and the order. Tell us if your line has a preference, for example a smooth inside face for cleaner discharge.
Will a coated bag stop my fertilizer from caking?
It helps by slowing moisture pickup through the walls. For a product that cakes badly, pair the coating with a liner and store filled bags off the floor, out of the weather.
Request coated fabric bulk bags
The spec from the label, the count and the ship-to ZIP. We confirm the spec, build the load and come back with the freight and the delivery window.