Duffle Top vs Spout Top Bulk Bags - Filling and Discharge Options

A duffle top bulk bag has a fabric skirt around the full top edge that opens almost as wide as the bag and is gathered and tied after filling. A spout top bulk bag has a closed top panel with a narrow tube that fits over a fill head. Duffle tops suit wide chutes, loaders and coarse products where speed matters more than dust control. Spout tops suit powders and filling stations that seal against the bag. The bottom is a separate decision that belongs to the plant emptying the bag.

At Cesur Packaging, founded in 1930, we build the top and base of our bulk bags around the equipment at both ends of the supply chain. Our 4-loop bags are made with a top spout or a top skirt, and the base can carry closures for remote, controlled or two-stage discharge.

What is a duffle top bulk bag?

A duffle top, also called a skirt top, is a fabric tube attached to the top edge of the bag body. It drapes over a chute or hopper rim during filling, then the operator gathers it above the product and ties it with a sewn-in cord. On our 4-loop bags this option is the top skirt, built for easy filling. Filling is quick because there is no spout to hook up, but dust escapes since the opening is rarely sealed against the feed.

What is a spout top bulk bag?

A spout top bag has a flat top panel with a filling spout sewn into its center. The spout slides over the fill head, where a clamp or inflatable collar holds it, and is tied off and tucked in after filling. In North American specifications a spout of 14 x 18 in (36 x 46 cm), diameter by length, is a frequent default, but the right size is the one that matches the fill head.

Product enters through a closed tube, so dust stays in the bag. Our 1 and 2 loop big bags can be built with an open top and filling spout, or with a filling spout that has a flap closure to hold back dust and particles during filling.

How do duffle top and spout top bags differ?

The open top, with no top panel at all, is the baseline: fastest to load and hardest to protect.

The deciding question is whether the filling point can be sealed. If it can, a spout top gives a dust-tight connection. If product falls from an open chute or bucket, a spout only slows the line and a duffle top fits better.

Bottom options for discharge

Flat bottom

A flat bottom is a closed base with no outlet. The bag is emptied by cutting the base over a hopper, so discharge happens all at once and the bag leaves service. Residue is low, but cut threads can fall into the product, and nobody should reach under a suspended bag to make the cut. Our 1 and 2 loop designs also offer a drawstring and flat bottom construction that cinches the base.

Spout bottom

A spout bottom is a discharge tube sewn into the base and closed with a tie, often under a protective flap. Retying or an iris closure throttles the flow, so partial discharge is possible. The weak point is residue, as cohesive powders tend to stay in the base corners around the spout. We build discharge spouts with standard or iris closures, and our 4-loop range adds:

• E-Knot, for remote discharging.
• B-Lock, for controlled discharging.
• Bonbon closure, a two-stage opening mechanism.
• Bottom cross, which supports the discharge tube.
• Hygienic cover, which keeps the discharge tube clean.

Materials that bridge or stick discharge poorly through any spout, and a full open base that releases the whole bottom works better for them.

Choosing by filling and discharge equipment

1. Fill head type. A clamp or inflatable collar calls for a spout top sized to it. An open chute, hopper or loader points to a duffle or open top.
2. Dust tolerance. Fine powders, food ingredients and chemicals in enclosed areas favor a spout top.
3. Discharge station. A spout access chamber or flow valve needs a spout bottom. A cut-and-dump hopper takes a flat bottom.
4. Dosing pattern. Batch dosing into a mixer needs a closure that can be controlled or retied. Emptying into a silo in one step does not.

Filling and discharge often happen at different companies, so the bottom should be agreed with the receiving plant before ordering.

Top construction on automatic filling lines

Depending on the product and the facility, a single operator can fill between 50 and 200 one-loop or four-loop big bags per hour on an automated line, so every bag has to present its top the same way each cycle. We manufacture bags for automatic filling in one-loop, four-loop and five-loop designs that can be fed from pallets or roll-fed winding systems into robotic filling lines.

Here the machine clamps the filling inlet, so spout diameter, length, position and folding pattern must match its pick-up sequence. A loose duffle skirt gives the clamp nothing fixed to grip. Our 1 and 2 loop bags, used for fertilizers, seeds, fish feed, cement powders and salt, can be designed for automatic filling machines and mainly carry about 1,100 to 3,300 lb (500 to 1,500 kg) where filling speed is critical. Liner choice for these lines is covered in our jumbo bags guide along with sizing.

Common mistakes in top and bottom specs

• Ordering a spout top without the fill head diameter. Too wide leaks dust around the clamp, too narrow can tear on the head.
• Filling to the rim. Roughly 10 to 15% headroom, about 5 to 7 in (12 to 18 cm) on a 47 in (120 cm) tall bag, leaves room to close the top.
• Specifying a spout bottom for a product that bridges.
• Choosing a flat bottom when the receiving plant doses in partial batches.
• Writing only "spout top, spout bottom" on the purchase order instead of diameter, length and closure type at both ends.

Questions buyers ask about duffle and spout tops

Can a spout top bag be filled without a filling station?

Yes, with a funnel or chute that fits into the spout, but filling is slower and the sealed connection is lost. For mostly manual filling, a duffle top is the better fit.

Does a duffle top hold more product than a spout top?

The skirt lets light material heap above the body line, so the bag takes more volume. The safe working load on the label still sets the weight limit.

Matching top and bottom to product and line

Our standard FIBC models cover filling capacities of about 1,100 to 4,400 lb (500 to 2,000 kg) with 5:1 and 6:1 safety factors. To match a combination to your equipment, contact our sales team with your fill head and discharge station details.