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Bulk bags are manufactured by weaving polypropylene (PP) tapes. This process involves several steps but it all starts with the mixing of raw materials and the extrusion of the PP. These tapes of high-tensile polymer are woven into a fabric, which is then sewn together to form the bulk bag and its accessories.

The following steps outline the extrusion process at Custom Bulk Bags

1.  The raw materials – PP granules, calcium carbonate and ultraviolet (UV) inhibitors – are mixed together in a large tray by our sister company, Integrated Polypropylene Products (IPP).

2. The mixture is then fed through a hopper into the extruder, where it is melted into a liquid form and, if necessary, a colour pigment is added. If no pigment is needed, the PP mix retains its semi-transparent white colour.

3. This molten liquid is then forced through an adjustable die to form a continuous flat strand of PP that solidifies rapidly in a cooling tank. The film is then slit with blades into tapes of various widths, as required.

4. These flat tapes are wound around industrial-sized bobbins, which can then be attached to a large weaving loom. This machine weaves the strands into a fabric that is strong and durable.

Our extrusion process for polypropylene tapes

5. The finished fabric is tested for tensile strength and quality. It is then delivered to Custom Bulk Bags, where we create the flexible containers (bulk bags).

The extrusion process is vital as it determines the quality and strength of the PP tapes. We only use industrial-grade PP tapes to manufacture our bulk bags. This ensures that our products have a minimum 5:1 safety factor, which means that our bulk bags can carry at least five times their intended load. For more information about bulk bags, please contact us today. 


Custom Bulk Bags is a South African manufacturer of woven polypropylene bags for various industries, such as mining, chemicals and food. We are able to produce over 3.5-million bulk bags per year, keeping our customers in stock at all times. Our bags adhere to the highest levels of quality as a result of our stringent in-house testing and quality control programmes.

Custom Bulk Bags holds ISO 9001 certification and we currently have a number of UN-certified designs. We are a Level 3 B-BBEE manufacturer and supplier and fall under the ownership structure of Deneb Investments Limited. For more information on our products, contact Follow us on Facebook for our latest news and industry insights.