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In the storage and logistics industry, there is a key aspect of materials that determines how they are handled and managed. This aspect is called bulk density and it applies to dry goods that can flow easily. Such materials are often stored or shipped in bulk bags because these lightweight storage containers are flexible, durable and able to carry up to two tonnes.

A product’s bulk density is its mass per unit volume in a bulk quantity. In essence, it is used to calculate the amount of material that can fit into a defined space, such as a bulk bag, metal container or cardboard crate. A product’s bulk density will determine many of the design features of a bulk bag, such as discharge attachments and the overall dimensions of the bag.

Custom Bulk Bags is a leading manufacturer and supplier of bulk bags in South Africa. Our products are tailored to your specifications and we can guarantee world-class quality and on-time delivery. All of our bags have a minimum safety factor of 5:1, which means that they can safely hold at least five times their intended load without tearing or breaking. We hold an ISO 9001 certification and we currently have a number of UN-certified designs in our line-up.

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Why is bulk density important?

Think about the consequences of miscalculating the bulk density of a large volume of material. At the very least, you would run out of bulk bags before all of the product is stored, but at the worst, you could put your employees and customers at risk if a bulk bag is filled with a load that is heavier than the bag can hold.

Failure to grasp bulk density can lead to unsafe storage and transport of huge volumes of material. Bulk bags could be put under a lot of strain, especially during the lifting and discharging phases. This calculation needs to be accurate for the safe handling of bulk materials.

What to look out for when it comes to bulk density

Bulk density can help you determine an accurate target weight for each bulk bag. This not only allows you to order the correct bulk bags from the start, but it also makes handling and shipping safer and easier for everyone involved. Keep in mind that the bulk density of some materials can fluctuate, due to the following reasons:

  • During the filling process, some materials may become aerated, which lowers their bulk density. In this case, you will need more bulk bags than initially calculated.
  • Some materials may compact during storage and shipping, which causes the material to decrease in volume. If bulk bags are stacked on top of one another, this can make them unstable and possibly tip over.
  • Moisture can seep into bulk bags if they are not fitted with an inner liner. This additional water increases the overall weight of the material in the bags, which can cause them to exceed their safe working load.
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How to manage these issues

Firstly, you need to know your materials quite well. If you know that a certain product is likely to aerate or compact, then you can factor this into your order of bulk bags. Similarly, if you know that your material is susceptible to moisture, then you can order bulk bags with a splash-proof inner liner that will keep the material dry at all times.

When choosing the best bulk bags for your needs, don’t be afraid to go overboard with the bags’ strength. Choose bags with a safety factor that is higher than necessary to make sure that they can hold the weight and that employees are not put in any danger while handling loaded bulk bags. This strategy can also give you peace of mind in the event that the bulk density is miscalculated or if the materials change density for any reason.

Lastly, ensure that you order the best discharge attachments for your product. Our team is on-hand for consultations and they will help you determine the best discharge attachments for your needs. Some customers require full-bottom discharges while others need spout attachments for a slower, more controlled release of the product.

Custom Bulk Bags can help you determine all the specifications of your order and ensure that they are delivered on time. We can help you work out the bulk density of your materials and offer advice on optional extras that you may require. For more information about our bulk bags or to consult with an expert, 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 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.