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Bulk bags are a vital packaging solution for various industries, such as agriculture, mining, construction and chemical production. Also known as flexible intermediate bulk containers (FIBCs), bulk bags are designed to store and transport large volumes of materials – many of which are powders or viscous liquids. This means that additional steps need to be taken to prevent these materials from leaking or seeping through the woven FIBC fabric.

When a bulk bag leaks, not only is valuable material lost but it can also lead to contamination and potential safety hazards. If flammable powders or hazardous materials escape through the bulk bag fabric, it can place employees at risk. It is, therefore, crucial to prevent bulk bags from leaking.

Custom Bulk Bags is a leading manufacturer and supplier of FIBCs in South Africa. We produce up to 3.5 million bulk bags per year, all of which have a minimum safety factor rating of 5:1 and are manufactured in accordance with international regulations and standards. We offer additional attachments to prevent bulk bags from leaking, such as inner liners, sift-proof seams and more.

Bulk bags being lifted off a trailer by a forklift

Why bulk bags can leak

The construction of bulk bags makes them strong, flexible and versatile. The fabric is made from woven tapes of polypropylene, but in between the crisscrossed tapes, there can be tiny gaps through which fine powdery substances or liquids can escape. This construction makes bulk bags breathable, but it necessitates additional components for fine substances.

There are other reasons why bulk bags can leak. Overloading the bags can put extra stress on the fabrics and make the minute holes between the tapes open up wider. Similarly, improper handling methods can distort the fabric when the bag is lifted up. 

Exposure to harsh environments or leaving uncoated bulk bags in direct sunlight can also weaken the polypropylene tapes, causing the fabric to leak or break. Lastly, poor construction materials and methods can result in leaks. By addressing these potential causes, you can ensure that your FIBCs work as intended for your powders and liquid materials.

A blue forklift picking up a loaded bulk bag from a large stack inside a warehouse

Preventing leaks in bulk bags

The first step to ensuring that your bulk bags do not leak is to inspect the quality upon delivery. Working with a reputable FIBC Manufacturer and supplier can help to guarantee the quality and construction methods, but if you’re not sure, always perform a close inspection of the woven fabric before filling the bulk bags.

Secondly, if you know that you need to store and transport fine powders or viscous liquids, then be sure to opt for inner liners. These can be made from plastic or foil and create a solid barrier that fits snugly inside the FIBC. Inner liners are highly effective at preventing leaks and can be sewn into the inside of a bulk bag or fitted loosely, allowing them to be removed and cleaned more easily.

Custom Bulk Bag employees fitting an inner liner into a bulk bag

Next, you can spec your bulk bags with sift-proof seams – also referred to as dust-proof seams. This is a special stitching method that creates a tight seal between the panels of a bulk bag, preventing fine particles of material from seeping through the seams. We recommend opting for this construction method if you’re storing sugar, fine fertilizer and other powders.

Lastly, to prevent leaks and breakages, proper handling techniques need to be followed at all times by employees. Do not overload FIBCs or use inappropriate lifting equipment as this can place extra strain on the fabric and seams. Ensure that bulk bags are stored in a shaded, dry environment – if they will be exposed to sunlight for extended periods, be sure to opt for a UV-resistant coating when placing your order.

Choose a reliable manufacturer and supplier, such as Custom Bulk Bags, to ensure that your FIBCs do not leak and meet your expectations. Our expert consultants are always on hand to guide you through the ordering and specification process. We are committed to supplying high-quality, durable and versatile bulk bags that meet the needs of our customers. For more information about our bulk bags, please contact us today.


Custom Bulk Bags is a leading 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 2 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.