Fertiliser bags and feed sacks: specifying a woven bag

Fertiliser bags and animal feed sacks are made from the same woven polypropylene (PP) fabric as a flour or rice sack, but they do not ask the same things of it. Fertiliser draws moisture out of humid air and cakes. Feed is bought partly on how clean and how clearly marked the sack looks. And sacks of both often wait in a yard or an open shed rather than a cool store, so sunlight, dust and rough handling count as much as the weave. This guide sets out what to decide before you ask for a quotation, and what to ask your supplier.

Key definitions

• Woven fabric. Flat polypropylene tapes interlaced at right angles, usually woven into a seamless tube on a circular loom. A closer weave leaves smaller gaps between the tapes.
• Fabric weight (GSM). Grams per square metre of fabric. More grams means more polypropylene: as a rule a stronger, stiffer and more expensive sack.
• Denier. The weight in grams of 9,000 metres of tape, which is how the weight of the individual tapes is described.
• Mesh. The number of tapes per inch, for example 10 × 10. A higher count is a closer weave.
• Liner. A separate bag of thin polyethylene film inside the woven sack. It holds fine material in and slows moisture.
• Lamination. A thin plastic coating bonded to the fabric, closing the gaps between the tapes.
• UV stabilisation. Additives in the tape that slow the damage sunlight does to polypropylene.
• Caking. Granules or powder taking up moisture and setting into lumps.

What fertiliser and feed ask of a sack

Four of the typical contents listed on our products page are farm and industrial inputs rather than food staples, and they do not behave alike.

Contents	How it behaves	What matters most	What to ask the supplier
Fertiliser	Granules that take up moisture from humid air and cake	Keeping moisture out; surviving re-handling	Closeness of the weave, fabric weight, a liner or lamination
Animal feed	Pellets or meal, in a sack the buyer judges by eye	Clean fabric and a legible print; dryness in store	White fabric, print quality, a liner for fine meal
Seeds	Light, valuable and usually sold by grade	Marking the grade clearly; letting the sack breathe	Coloured stripes or print for each grade
Chemicals and minerals in powder or granules	Fine or abrasive, heavy for their volume	Sifting through the weave and the seam; abrasion	A closer weave or lamination, and the bottom seam

Fertiliser is the demanding one. Many common fertilisers take up water from humid air, and once the granules have taken it up they set into a block that no longer flows on a filling line. Woven fabric on its own is not a barrier: air and moisture pass between the tapes, which is why liners and lamination exist. Both are options that exist in the trade and that not every maker supplies, so ask your supplier what it can provide and what it advises for your product. Then fill sample sacks and keep them for a few weeks in the conditions your real stock will see.

Feed is judged differently. A farmer or a dealer reads the sack: the product name, the mix, the net weight and the brand. White fabric keeps that print legible, which is why feed plants usually order white woven bags even for goods that never reach a shop shelf.

Sun, stacking and handling

Filled sacks of fertiliser and feed are often stacked in a yard or an open shed, sometimes for a whole season. Two things follow from that.

Sunlight is the first. Polypropylene degrades under prolonged sun unless the tapes are UV-stabilised: the fabric loses strength, and a sack that was sound when it was filled tears when it is lifted. If your sacks will stand outdoors or travel uncovered, say so when you ask for a quotation and ask about UV stabilisation.

Handling is the second. A sack of granules is heavy, is dragged and dropped more often than a sack of flour, and the granules themselves can be abrasive. What fails first is the bottom seam or a corner. Ask what the fabric weight is, how the bottom is closed, and whether a double row of stitching is available for your sack.

Stack filled sacks in interlocking layers, off the floor on pallets and under a roof where you can. Keep empty sacks the same way: a bale left in the sun before it is ever filled has already lost part of its life.

What goes on the sack

What must appear on a fertiliser or feed sack is set by the country where the goods are sold, not by the bag maker. Buyers usually print the product name, the grade or mix, the net weight, the packer’s name and a space for a batch mark. Check the rules of the destination country, then send your supplier artwork that already carries what those rules require. Our guide to preparing artwork explains how to supply it and what a proof is for.

If you would rather identify sacks without print — a trader repacking, or a plant moving material between buildings — unprinted bags in white or coloured fabric do the same work, and coloured stripes woven into the fabric can mark a grade without any printing at all.

Specifying the sack, step by step

1. Product and fill weight. For example: compound fertiliser, 50 kg per sack. 25 kg and 50 kg are common fill weights for both fertiliser and feed.
2. Size. Width and length of the flat sack, in centimetres. If a sack you use already works, measure it flat and send those two figures.
3. Protection. How long the sacks are stored, how humid the route is, whether they stand in the sun, and whether a liner, lamination or UV stabilisation is advised and available.
4. Fabric colour. White, a colour, or white with coloured stripes woven in to mark a grade.
5. Print. Unprinted or printed, with the artwork and where on the sack it should appear.
6. Top and bottom. Hemmed or heat-cut top, how the bottom is sewn, and how you close the sack after filling.
7. Quantity and destination. The number of sacks, whether the order will repeat, and the place of delivery.

Steps 1, 2, 4, 5 and 7 are the six details Al-Sharq Plastic Manufacturing Company needs to prepare a quotation.

Ask rather than assume

Al-Sharq Plastic Manufacturing makes polypropylene woven bags — white and coloured, printed and unprinted — to each buyer’s requirements, at its plant in 10th of Ramadan City, Sharqia Governorate, Egypt. The factory page shows the tape extrusion and stretching line, the winders and the circular looms the fabric comes off.

Fabric weights, liners, lamination and UV stabilisation are options in the trade, and this website does not publish which of them suit any given sack. Describe your product, your storage and your route through the enquiry form and ask. It is the same question you should put to any supplier.