How PP Woven Bags Are Made — From Granule to Bale

A PP woven bag starts as polypropylene granules. The granules are extruded into a thin film, chilled, slit into narrow tapes, then stretched in a hot-air oven. That stretching orients the polymer chains and is what gives the finished tape its tensile strength.

The tapes are wound onto bobbins and fed into circular looms, which weave them into a continuous tube of fabric. Mesh count (for example 10x10 or 12x12 strands per inch) and denier together decide the fabric GSM — and therefore the safe working load of the bag.

If the contents must stay dry, the tube passes through a lamination line where a thin BOPP or PE film is coated onto the outer face. Printing is then done either flexographically on the woven fabric or by laminating a pre-printed BOPP film for photo-quality artwork.

Finally the tube is cut to length, bottom-hemmed and stitched (or heat-cut and sewn with a valve, in the case of cement bags), bundled and baled. Every stage is a place where a cheaper supplier can quietly cut cost — under-stretched tape, low mesh count, recycled content in the tape. Ask for tape denier, mesh and GSM in writing before you compare prices.