PP woven sacks buying guide: GSM, mesh, lamination and liners explained

Polypropylene (PP) woven sacks carry a huge share of the world's bulk goods: cement, fertiliser, rice, sugar, flour, animal feed, chemicals and plastic granules. They are cheap, strong and light, but only when the specification matches the product. A sack that is a few grams too light can split on the loading line. One that is too heavy wastes money on every bag, and you buy thousands.

This guide explains the specifications that matter, so you can compare quotes properly and avoid failures.

How woven sacks are made

PP granules are melted and extruded into a thin film, which is slit into narrow tapes and stretched to make them strong. The tapes are woven on circular or flat looms into fabric. The fabric is then optionally coated or laminated, printed, cut and stitched into bags.

Almost every specification on a woven sack quote describes one of these steps.

The key specifications

Fabric weight (GSM)

GSM is the weight of the woven fabric in grams per square metre. It is the main driver of strength and of price. Lighter fabrics suit small, light loads; heavier fabrics are used for 50 kg sacks of dense products like cement or fertiliser. Quote comparisons only make sense at the same GSM.

Mesh (weave density)

Mesh describes how many tapes there are per inch in each direction, for example 10x10 or 12x12. A denser mesh gives a tighter, smoother fabric that holds fine powders better and prints better.

Tape denier

Denier measures the weight of the individual tapes. Together with mesh, it determines the GSM and the feel of the fabric. You don't always need to specify denier, but if a supplier hits your GSM with an unusually coarse or fine tape, ask why.

Bag size

Give the width and length of the finished bag, and say whether the length is measured before or after stitching. Size depends on the product's bulk density and the fill weight, so a 50 kg bag of flour is bigger than a 50 kg bag of cement.

Coating and lamination

• Unlaminated (uncoated) sacks breathe, which suits products that need air flow, such as some grains or onions. They let fine powder and moisture through.
• Coated or laminated sacks have a thin PP or PE layer that blocks dust leakage and moisture. They are standard for cement, fertiliser, sugar and fine chemicals.
• BOPP laminated bags have a printed BOPP film laminated onto the woven fabric. They give photographic-quality print and are used for retail packs of rice, flour, feed and pet food.

Liners

An inner LDPE or HDPE liner gives extra protection against moisture or contamination. Liners can be loose or stitched in. Specify the liner thickness (in microns) and whether it should be food grade.

Stitching and closures

• Bottom stitching: single fold or double fold, single or double stitched. Double fold and double stitch is stronger for heavy loads.
• Mouth: open mouth for sewing after filling, or valve bags (common for cement) that fill through a valve and seal themselves.
• Hemming of the mouth stops fraying and makes filling easier.

UV stabilisation

PP degrades in sunlight. If bags will be stored outdoors or shipped through hot climates, ask for UV-stabilised fabric and state roughly how long the bags must last in sun exposure.

Food contact and certifications

For food products, ask for food-grade raw material and a declaration of compliance from the supplier. For export, buyers may ask for test reports on drop strength, tensile strength and seam strength. In India, BIS standards cover several woven sack applications such as cement and food-grain packaging; ask which standard the supplier tests to.

FIBC (jumbo) bags

Flexible intermediate bulk containers (FIBCs, or jumbo bags) are woven PP bags that carry 500 kg to 2 tonnes. They are specified differently:

• Safe working load (SWL) in kg.
• Safety factor: commonly 5:1 for single-trip bags and 6:1 for multi-trip bags, meaning the bag is tested to several times its SWL.
• Top and bottom design (spout, duffle, flat), loop type, and whether a liner or baffles are needed.
• Electrostatic type (A, B, C or D) for flammable or dusty products.

What makes the price

• GSM, size and quantity (raw PP is the largest cost)
• lamination, liner and UV additives
• number of printing colours and sides
• stitching type
• packing (bales of 500 or 1,000 bags, palletised or loose) and freight

Raw PP prices move with crude oil and petrochemical markets, so ask how long a quote is valid.

Checks on delivery

• Weigh a sample of empty bags; average weight should match the agreed GSM and size.
• Measure bag dimensions.
• Check the print for colour, registration and spelling.
• Fill test bags and drop-test them from a set height.
• Check seams for skipped stitches.

A specification template

When you ask for quotes, include:

1. Product to be packed and fill weight.
2. Bag width and length.
3. Fabric GSM and mesh.
4. Laminated or unlaminated; BOPP or not; liner type and thickness.
5. Colour of fabric; print colours and sides.
6. Stitching and mouth type; valve or open mouth.
7. UV stabilisation if needed.
8. Quantity, packing, delivery location and date.

Frequently asked questions

What GSM do I need for a 50 kg bag?

It depends on the product's density, how the bags are filled and handled, and how far they travel. Dense powders like cement and fertiliser need heavier fabric than grains. Ask suppliers to recommend a GSM and run filling and drop tests with sample bags before ordering in bulk.

What is the difference between laminated and BOPP bags?

A laminated bag has a plain PP coating on the woven fabric to block dust and moisture. A BOPP bag has a printed BOPP film laminated on top, which gives high-quality multicolour graphics for retail packs.

How long do woven sacks last in sunlight?

Standard PP degrades within weeks to months in strong sun. UV-stabilised fabric lasts much longer. If bags will be stored outdoors, specify UV stabilisation and the expected exposure time.

Can woven sacks be recycled?

Yes. PP woven sacks are recyclable where collection exists, and many manufacturers use recycled PP in non-food applications. For food contact, use virgin food-grade material.

Find woven sack manufacturers on GlobalMart

Compare manufacturers in woven sacks, and related suppliers in flexible packaging, pouches and industrial packaging. Or post your requirement with the template above and let suppliers come to you.