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Principles of FIBC Bulk Bag Filling: Design & Handling

FIBC Bulk Bag Selection & Filling Guide: Principles of Design & Handling

Spiroflow Gain-in-weight C3 Bulk Bag Filler

What are FIBC bulk bags, what are they used for and why are they important?

FIBCS, also known as bulk bags or big bags or super sacks, are made of tightly woven strands of polypropylene, a flexible fabric designed for storage and transportation. These woven, flexible bags hold dry, flowable materials, ingredients and powders across industries including but not limited to: food and beverage, plastics, pigments, chemicals, pharmaceuticals, grains, construction materials, salt, peanuts, seeds and minerals. 

Unlike smaller, dusty 50 lb.bags that are now dwindling in popularity, most FIBC bulk bags are built to hold at least 2,000 and up to 4,000 lbs. of product and protect operators with dust control solutions in both the filling and unloading processes. With the reduction in the number of bags needed for filling, storage and emptying (due to each bag holding more product) and the introduction of a flexible solution (vs. traditional rigid containers) comes a laundry list of benefits. 

It’s no surprise that the global flexible intermediate bulk container (FIBC) market size is expected to reach $6.4 billion by 2026. As more and more products are supplied in FIBCs, all aspects of the bulk bagging system, including bulk bag filling, discharging, and conditioning become increasingly important. 

“The global flexible intermediate bulk container (FIBC) market size is expected to reach $6.4 billion by 2026”

Benefits of FIBC Bulk Bags

FIBC bulk bags are growing in popularity as a bulk transportation and storage solution (vs. using traditional smaller bags and rigid boxes or drums) due to the benefits of bulk bags including:

  • Safe and easy handling – Bulk bags are filled at the top and emptied at the bottom vs. tipped over, improving operator safety. Further improving safety are integrated dust collection systems available for bulk bag fillers and workers. Additionally, bulk bags are not moved manually by workers, but instead are moved by forklift or pallet jacks, minimizing risk for the operator due to there being no direct contact. 
  • Reduced storage, shipping and labor costs – Fewer bags means fewer trucks to ship, fewer bags to move and stable bags mean operators can stack bags 2 high on the plant floor saving on storage room. Additionally, the bulk bags themselves, once emptied, can be folded and stored at the facility using minimal space vs. a rigid container like a box or drum.  
  • Minimum risk of product damage or loss. The polypropylene flexible material is more tear and puncture resistant vs. rigid containers, which protects the contents from damage or loss from material leaking out of the bag. Additionally, the filling and unloading process for bulk bags reduces the risk of spillage vs. the tipping motion needed to unload rigid containers that must be both filled and unloaded from the top. 

Who uses FIBC bulk bags?

FIBC bulk bags are used as a packaging unit for bulk bag filling by many different companies and organizations. Each is interested in safe and easy handling, reduced costs and minimum risk of damage or loss, as described in the benefits section above.  

Examples of Companies That Use FIBC Bulk Bags: 

  • Suppliers and manufacturers of products to be discharged into FIBCs
  • End Users and Buyers of products supplied in FIBCs
  • Companies using FIBCs as a handling unit within their own plant
  • Custom packers receiving products in bulk for packing into FIBCs
  • Transportation/Shipping/Storage companies handling FIBCs

FIBC Bulk Bag Design & Filling System Guide

“The Choice Of FIBC Is Critical, Both With Regards To Design & Size As The Most Expensive Part Of An FIBC Packaging System Is The FIBC Itself.” 

This informative Spiroflow guide will support you in your next FIBC purchase and bulk bag filling system design. Below we cover considerations for FIBC bulk bag selection (size, shape, loop system, spout, outlets and liners), bulk bag handling and bulk bag filling. Proper bulk bag design and the engineering of the bulk bag filling system are the difference between lumpy, uneven, unsafe bags and densified, flat-top, safe bags.

FIBC Bulk Bag Design: Determining FIBC Size & Shape

When determining the bulk bag size, the following criteria must be considered for the bulk bag filling system:

  • Product weight in the FIBC bag
  • Product tamped bulk density
  • Internal dimensions of the shipping container or vehicle on which the FIBC will be transported
  • The net filled height of the FIBC (after filling)

When determining the bag shape remember:

  • Rectangular base FIBCs will round out during filling in their mid-section
  • Square or panel bags do not round out as much 

To determine the correct base size and shape, the internal dimensions of the shipping container or trailer should be evaluated to ensure a “push fit.” ISO containers are usually 7 ‘ 6” wide internally. 

“Push fit” means that when placed side by side in a container/trailer the exterior side of the bags touch the container wall and the interior sides touch each other.  This prevents the bags from shifting during transport.

To place two FIBCs side by side across the container/trailer, use the following formula: 

Maximum FIBC Base width = (3.14 X Internal Width of Container or Trailer)/(8 x (1 + Stretch Factor)) 

FIBC Rounded Out Diameter = (2x (Base length + Base width) x (1 + stretch factor)) / 3.14

Stretch Factor: 

The stretch factor can vary depending on the tightness of the weave of the FIBC fabric being used, the structural design of the bag and the density of the filled product. Generally, a figure of 3% – 5% should be used. 


FIBC Manufacturer Relationship

To arrive at the base size that will fit the selected method of transportation, a close liaison with the FIBC manufacturer is required to ensure that they can supply the right size. The height of the bag depends on the filled density, the weight required and any height restrictions placed on the FIBC by the user. 


Storage & Transportation Considerations

Where storage of filled bulk bags plays an important cost factor for both the filler and the discharger, the following should be considered:

  • Safe Stacking Height – For safe stacking of FIBCs it is not advisable to stack bags two high if the bags are over 5’ high and three high if they are over 4’ high – regardless of whether they are on pallets or not. FIBCs should not be higher than twice the base plus width. Additionally, leveraging a bulk bag filler that results in higher densification should be considered to produce a flatter bag top, which is more stable for stacking.
  • Test Filled Height – The filled height of the product in the FIBC after filling can vary considerably depending on the type of filling machine used and the characteristics of the product. It is important to get the product tested on the selected filling machine before ordering FlBCs. Bulk bag filling machines that have the capability of densifying the product during filling save on FIBC height and make a safer and more stable FIBC for stacking and handling.

FIBC Bulk Bag Design: Selecting & Sizing Lifting Loops, Spouts & Outlets

Lifting Loop Options

Lifting loops are usually located at the top four corners of the FIBC and are used to lift up and move the bag. They may also be of the ‘Cross Corner‘ type. ‘Pop Up’ loops help to enable a fork lift truck to engage the loops without additional labor, but they do incur additional costs. The length of the loop is generally 10” but may increase to 12” if the FlBC is to be picked up and moved by fork lift truck tines. 

Filling Spouts

Bulk bag fill spouts are tailored to fit the filling machine head. When liners are used, some machines clamp only the liner, in which case the diameter of the filling spout can be increased to 20 – 24” to allow the product to reach the ‘shoulders of the FIBC’ and not bridge in its neck. This is most important with powders. A 15” diameter is the most com-mon filling spout diameter.\

Outlet Spouts 

The diameter of the outlet spout should be enough to insure the easy discharge of filled product from the bulk bag. Diameters tend to vary between 10” and 24”. Outlet spout length should be enough to ensure that it can be tied off and in most cases goose-necked. The length can vary from 16-36” dependent on the diameter.

Ease of discharge is also assisted by the correct design of the discharge machine. Most modern-day bulk bag discharge units can handle poor flowing products, depending on their design and choice of product flow promotion device. 

Other FIBC Outlet Systems

These are many and various, but all are designed to accommodate a product or discharger type that cannot be overcome by a standard outlet spout.

  • Flat Bottom
  • Conical Bottom
  • Hygiene Flaps and Hygiene System
  • Fully Bottom Opening Bags


FIBC Bulk Bag Design: Liners

Lined FIBCs/bulk bags are usually used for fine powders, food and pharmaceutical products. Liners are only rated as moisture proof and not waterproof. Polythene will allow the ingress of moisture over a period and require careful attention to properly tie the bag off after filling. Standard design liners are normally extruded in a tube. The circumference of the extruded tube should be equal to the base perimeter of the FIBC plus 2% to eliminate over stretching. Liners are normally manufactured from linear blend polythene as it is stronger than low density polythene and reduces the risk of shredding or crumbing when it is cut. Liners are between 5/16“ thick dependent on the product and the protection required. These liners are only suitable for products being filled with a temperature not greater than 176°F as they will start to plasticize above this temperature. For temperatures above 176°F, special liners should be used.


FIBC Bulk Bag Design: Bag Construction & Quality

FIBCs are designed to be lifted by their loops when filled and strength is built into the FlBC to give a safety factor of 5:1 for single trip bags and 6:1 for multi-trip (used more than once) bags. UN Chapter 16 FIBCs are tested to a safety factor of 8:1. FIBCs designed to hold food or pharmaceutical products should be manufactured in such a fashion to ensure loose cotton ends or frayed material from hand cut areas do not occur. Outlet spouts should be hemmed, and tie cords should have ‘flames’ ends.


FIBC Bulk Bag Handling

Pallets are by far the easiest method of moving filled FIBCs. The following considerations are important for safe and efficient movement by pallet: 

  • The correct size of pallet should allow the rounded section of the FIBC to overlap the edges of the pallet so that when two palletized bags are placed side by side, the bags touch and not the pallets. This increases stability of the bags when packed in containers/trailers.
  • The FIBC should be positioned as close to a central position on the pallet as possible, especially after filling. A wide range of mechanical devices to assist the fork lift truck driver to achieve this are available as well as side shift on the truck itself.
  • If the FIBCs are to be stacked, close slatted pallets, both top and bottom should be used to stop ‘pinching’ of the bag by allowing the top and the bottom of the FIBCs to protrude through the slats. These tend to be expensive and may only be financially justified for ‘in plant’ use unless return of them can be guaranteed.

Tamped Bulk

Density l


Untamped Bulk






Aluminum Chips




Aluminum Oxide




Ammonium Nitrate




Baking Soda




Barium Soda




Portland Cement




Wheat Flour









Particle shape as well as size plays an important part in the time it takes to remove entrained air. Plate shaped particles, of clays for instance, take three to four times the amount of vibration to remove entrained air than a similar sized round particle. Granular particles will lose their entrained air quickly under their own weight. The larger the granule, the shorter the time it takes to get to a tamped bulk density. Even then, vibration will ensure added stability is achieved. Vibration will only act on the weight of the material above the weight of the vibration platform. Therefore, vibration should not be commenced until a minimum weight of 450 lbs. is in the FIBC.

Principles Of Bulk Bag Filling

During the development of FIBC bulk bag filling machines, certain basics have been identified that must not be overlooked when filling FIBCs. 

  • Correct position of empty FIBC bulk bag in relation to machine base – All woven polypropylene bags will stretch to some extent during filling when hung by their loops. The FIBC should be positioned so that the seams of the FIBC can stretch down during the filling cycle, with the actual comers of the bag only touching the base when the fill cycle is complete.
  • Base Vibration for Densification – The bulk density of the product in the filled bag should be as near as possible to its tamped bulk density. This should be achieved while the FlBC is awaiting removal from the filling machine.
  • Fill Rate Control and Displaced Air Exhaust – Complete control of the product passing through the filling head must be maintained to facilitate a steady filling rate. The filling head must also allow for the exhaust of displaced air to prevent dust and pressurization of the FIBC during filling.
  • Liner Inflation & Attachment to the Filling Head (Slip Seal) – For FIBCs with liners, inflation is particularly necessary prior to filling. The liner needs to be sealed to the filling head to insure there is no dust release. However, during inflation and filling the liner must also be free to move inside the FIBC and take up the shape of the bag without stretching. To extend product storage life, consider purging the bag of oxygen using nitrogen purging prior to filling. Oxygen feeds on bacteria. Thus, a nitrogen purge and heat-sealing process can significantly extend stored product life. 
  • Robust construction – Robust construction will ensure long life and protection from potential damage from fork lift trucks.
  • Operator Access – Ensure operator ease of access to:
    • Attach the loops to the FIBC Support Arms
    • Connect the filling spout/liner to the filling head
    • Disengage the filling spout/liner from the filling head.
    • ‘Tie off’ the filling spout  (The operator should be able to carry out all of these functions at shoulder height without the need to climb on the machine)
    • Electrical controls (Preferably microprocessor based (compact) and easily accessible by the operator. All bag filling functions should be able to be performed manually (as required by the operator) and automatically (once the filling cycle is initiated).

Bulk Bag Filling Automation

The above basic bulk bag filling principles have been augmented by options designed to automate the filling operation and reduce operator involvement. These developments have enabled an increasing number of products to be handled in FIBCs, leaving the future open for more companies to benefit from the advantages offered by this form of packaging.

  • Pallet Magazine/Stacker – Several pallets can be placed ready for the filling operation to commence. This equipment then selects a lone pallet from the stack to be sent to the filling machine.
  • Slip Sheet Dispenser – A slip sheet is then placed on the pallet automatically prior to filling.
  • Automatic Bag Loop Release – Once the bag is filled it is automatically released from the filling machine ready for automatic removal. Take Off/Accumulation Conveyor – The filled bag is then conveyed away, allowing a new bag to be placed ready for filling.
  • Spinning Head – This is an attachment to the filling head suitable for use with ‘baffle’ bags and granules where vibration alone is not capable of both de-aerating and dispersing the product. The Spinning Head disperses the product stream as it enters the bag to achieve an even fill.


The choice of FIBC bulk bagging system is critical, both with regards to design and size, as the most expensive part of an FIBC packaging system is the FIBC itself. The wrong choice is not only expensive in terms of product waste and high labor costs but could also lead to a loss of customer confidence in FlBC bulk bagging solutions. To choose a standard size at a reduced price that does not suit the exact needs and those of a customer can lead to a system that will not meet your application or needs. Trials should always be conducted on the chosen filling equipment, taking into account shipping, storage, fill weight requirements, bagging rate requirements and any special considerations for the specific flowable material or application.