Big bag discharging options: bottom and outlet systems
Choose a bottom design that matches the discharging station of the end user, from a plain flat bottom to a protected outlet spout or a full-width skirt.
Flat bottom, outlet spout, bottom skirt or conical bottom: the bottom design of a big bag determines how it is emptied, how fast and whether it can be closed again.
The bottom of a big bag (FIBC) is built in one of four ways: a flat bottom that is cut open or tipped, an outlet spout for controlled discharge, a bottom skirt that opens the whole base, or a conical bottom that funnels the product into the spout. The outlet spout is the standard, available in diameters from 25 cm to 65 cm with several tie styles and protective closures.
DIV Trades manufactures all bottom types in-house and combines them freely with every inlet type, loop type and sealing level. The end user's discharging equipment should decide the design, so ask your customer how they empty the bag before you order.
FIBC bottom types compared
Flat bottom
A closed bottom without an outlet. The bag is emptied by cutting the bottom open or, in the construction sector, by tipping it over. It is also used for waste that is buried or incinerated together with the bag.
- The cheapest big bag bottom
- Nothing to tie or protect during transport
- Single use only, the bag is destroyed when emptied
- No control of the material flow
Outlet spout
The standard way to empty a big bag. Spout diameters range from 25 cm to 65 cm; the spout length should be at least equal to its diameter, and 50 cm is standard. The spout is tied closed for transport and opened over the discharging hopper.
- Controlled, dust-reduced emptying
- The bag stays intact, so partial emptying is possible
- Fits standard discharging stations
- The spout must be protected or tied carefully so it is not damaged in transit
Bottom skirt
A skirt opens the complete bottom of the bag. Because the skirt itself cannot carry much load, it is usually combined with a flap or a star-type closure. Bottom skirts suit materials that are hard to discharge through a spout, such as sawdust or peat.
- The whole bottom opens for fast emptying of bulky or bridging materials
- Needs a load-bearing flap or closure underneath
- Less control of the material flow
Conical bottom
The bottom is tapered towards the spout so the whole product flows out. Products that tend to collect in the corners of a standard bag would otherwise force the operator to shake the bag.
- Complete emptying without shaking
- Faster discharge of poorly flowing products
- More fabric and sewing than a flat bottom with spout
Tie styles for the outlet spout
- Standard tie: a 60 cm tie sewn in the middle of the spout, folded and knotted.
- Swan neck: the spout is folded twice and tied, which gives a tighter closure for fine products.
- B-lock: a plastic lock with a band on the spout, suitable for manually regulating the material flow during discharge.
Protecting the outlet spout during transport
Outlet spout with rosette closure
Light-fabric petals sewn around the spout and tied over it. With the rosette closed the bag looks like it has a flat bottom, and the spout is protected from damage during transport and handling.
- Low-cost spout protection
- Bag stands flat on the pallet
Outlet spout with star closure
A rosette variant made from heavy fabric and shaped like a star. It is sturdier than the light-fabric rosette.
- Stronger protection from heavy fabric
- More expensive than a rosette
Double outlet spout
A second spout around the inner spout. The outer spout shields the inner one during transport and handling.
- Protects the inner spout
- Two spouts to open at discharge
Outlet spout with flap
A heavy-fabric cover attached to the bottom with a band. It protects the bottom of the bag from moisture.
- Moisture protection for the whole bottom
- One extra step when opening the bag
Closures for bottom skirts
Skirt with flap
The flap carries the load of the bag. It is made from heavy fabric, sewn to one side of the bottom and tied to the remaining three sides.
Skirt with letter closure
A rosette cut in the shape of a letter, made from heavy fabric, which protects and supports the skirt until the bag is opened.
Spout length rule
The outlet spout should be at least as long as its diameter, otherwise it cannot be tied securely. A 40 cm spout is therefore at least 40 cm long; the standard length is 50 cm.
What is the standard outlet spout size on a big bag?
A diameter of 25 to 65 cm with a length of at least the diameter; 40 cm × 50 cm is a typical size, as used on our stock big bags.
How is a flat-bottom big bag emptied?
By cutting the bottom open or tipping the bag over with the help of bottom loops. The bag is used once and is the cheapest FIBC design.
Which bottom is best for sawdust, peat or other bridging materials?
A bottom skirt with a flap or letter closure. It opens the entire base of the bag so the material cannot bridge above a narrow spout.
How do I stop the outlet spout from being damaged in transport?
Order a rosette, star closure, double spout or bottom flap. All four cover the tied spout so it cannot be caught by forks or pallets.
Can I regulate the material flow while discharging?
Yes, with a B-lock tie: a plastic lock on the spout band lets the operator open and close the spout by hand during discharge.
Which outlet does your customer need?
Tell us how the bags are emptied and we will design the bottom, spout size and closure to match, with samples on request.
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