Bulk Density vs. Particle Density: What’s the Difference?

To the untrained eye (or ear) the terms “bulk density” and “particle density” can sound very similar. We asked our trusty materials scientists about the differences between bulk density vs. particle density and what they mean for you and your sustainable packing strategy. 

Bulk density vs. particle density: What is bulk density? What is particle density? 

Time for some scientific definitions. Don’t worry: We’ll make this simple, short, and sweet!

The bulk density of a product is its mass per unit volume of granules or powders when considering that material in a bulk state. In the bulk packaging world, we use the defined bulk density of a substance to figure out just how much of that substance we can fit in a specific size of bulk bag. A product’s bulk density will influence many different aspects of the bag design you go with, including its size, strength, discharge options, and more. 

The particle density of a product accounts for the mass and volume of only the solid particles of a given substance. Particle density does not take into account the water and air that may be present in any given amount of product. 

In other words, if we’re looking at a container of soil, the particle density of that soil will convey information about only the specific soil’s solid particles. The bulk density, on the other hand, will provide a much more comprehensive picture of the amount of room the soil requires because it takes into account aeration and moisture. 

How do you measure a product’s bulk density and particle density?

Let’s say that you have the accurate weight of a sample of soil. 

In order to measure the soil sample’s bulk density, you would divide the weight of the soil sample by the overall volume (e.g., how much room that soil sample is taking up) easily measured in a container such as a graduated cylinder. 

In order to measure the soil sample’s particle density, you would need to figure out how much room only the soil’s solid particles are taking up. Often, people do this by suspending a very specific amount of soil in a specific amount of water and then subtracting the water’s volume from the total. 

Since the particle density won’t include water or air, the particle density for a substance is usually larger than the bulk density. Think of it like large metal blocks. The density of that one block (all metal) would be higher than if you were to have a bag of metal blocks as the spacing between this block is taken into account.

Even though these two terms can sound similar, don’t confuse them! Why? 

Think about what might happen if you designed a bag for a product based on a substance’s particle density instead of keeping its bulk density in mind. The bags would likely be far too small—or we would make the bags much stronger than they need to be, which may not be a great use of resources. Your FIBC supplier should be able to produce bags that work seamlessly with both your product and your filling, storing, and shipment processes. 

Wondering how they do this? Let’s talk briefly about how to make sure your bulk bags work well with your specific product’s properties. 

How can density help you determine your bulk bag specifications?

First of all, when you’re customizing your bulk bags with your supplier, notice whether they ask you detailed questions about the physical properties of your product and the environments you plan on storing and shipping your products in.

This may seem like overkill, but it’s an indication that your supplier is doing its job well. To make bags that are the right size and durability for you, the materials scientists on your FIBC supply team will need to know your product’s bulk density. They’ll also need to consider whether any of your frequent processes could change that bulk density. 

For example, some filling systems can add a lot of air in and around a product’s particles. Similarly, if a bag is going to be in a moist environment, the materials scientists will need to either coat your bulk bag to protect your product from moisture, account for the potential moisture in bulk density calculations, or both. 

Ultimately, your dream bag supplier will go above and beyond to take the guesswork out of purchasing the right bulk bags for you. When it’s time to order your bags, just make sure you have the bulk density of your product on hand; it’s a number that can be a big deal for your bulk packaging strategy! 

Rely on the materials experts at Conitex Sonoco to help you customize your FIBCs flawlessly.

When it comes to bulk density vs. particle density, the seemingly small difference between a few different physical properties can make a big difference in the way you customize your bags! Fortunately, you don’t have to figure out how to build the best bulk bag for your processes on your own. Simply give your bag supplier as much information as possible, and they’ll take it from there! 

Interested in ordering high-quality, customizable bulk bags? Learn more about our FIBCs at Conitex Sonoco and place your order today!