Sewn Open Mouth Paper Bags: 7 Buyer Checks

A sewn open mouth paper bag looks simple: a tube of paper, a pre-closed bottom, and an open end you sew shut after filling. That simplicity is exactly why buyers get burned. Two bags can look identical on a quote sheet and behave completely differently on a fill line running 20 bags a minute. If you are sourcing sewn open mouth paper bags for feed, seed, fertilizer, minerals, chemicals, or building materials, the details that decide whether your line runs or jams are buried in the structure, not the price.

This guide covers the seven checks that separate a bag that works from a bag that costs you product, downtime, and rework. It is a companion to our broader Multiwall Paper Bags Buying Guide: 7 Smart Factors to Check, which covers the full multiwall category. Here we stay focused on the sewn open mouth construction specifically.

What a Sewn Open Mouth Paper Bag Actually Is

A Sewn Open Mouth bag, usually shortened to SOM, is an open mouth bag that is closed with sewing thread. The bottom is pre-closed by the bag supplier. The user fills the bag through a hopper or vertical filling spout, then sews the flush cut open end shut.

SOM bags are one of the oldest multiwall bag constructions still in wide use, and they remain a cost-effective, durable option for a broad range of dry flowable products. They work with both manual and fully automated packing equipment, which is a big part of their staying power: a plant can start with hand-fed sewing and scale into a fixed sewing head without changing the bag style.

Typical applications include animal feed, rice, seed, fertilizer, pet food, minerals, chemicals, poly resins, yard waste, building materials, food products, and abrasives. If your product pours, SOM bags are probably on your shortlist.

Check 1: Paper Type, Kraft or Extensible

This is the single most misunderstood decision in multiwall paper bag sourcing, and it drives both performance and cost.

Property	Traditional Kraft Paper	High Performance Extensible Paper
Wood fiber	Short fiber	Long fiber
Sheet character	Heavy, coarse	Smooth
How it gets strength	Higher basis weight	Superior stretch and flexibility
Stretch	Limited	6 to 7 percent
Porosity	Low	High
Energy absorption	Limited	Superior
Typical construction	3 to 4 ply	2 ply

Kraft paper is the traditional workhorse. It is heavy and coarse, and it earns its strength through basis weight. Extensible paper is made from long wood fiber, which gives it a smooth sheet that stretches and absorbs energy rather than tearing. That energy absorption matters most in drop tests and rough handling, where a bag hits a conveyor or pallet corner.

Neither is automatically better. A four-ply kraft bag and a two-ply extensible bag can both be correct answers for the same product. What matters is that your supplier can explain why they recommended one over the other for your fill weight and handling profile.

Check 2: Ply Count and Basis Weight

Ply count is the number of paper layers in the bag wall. More plies generally mean more strength, but also more material, more cost, and a stiffer bag that can be harder to handle on some equipment.

Ask your supplier to walk you through the ply structure ply by ply, not just the total. A bag described as “three ply” tells you nothing about whether the outer ply is a printable bleached sheet, whether there is a moisture barrier layer, or whether the inner ply is food grade. Those details affect print quality, shelf life, and regulatory compliance.

• Fill weight: heavier fills need more total paper strength.
• Product density: dense minerals stress a bag differently than light seed.
• Handling: manual palletizing punishes bags more than a robotic palletizer.
• Moisture exposure: humid climates and cold storage change the requirement.

Check 3: Closure Method and Sewing Equipment

This is where SOM bags earn their name, and where a lot of operational headaches start. There are three common closure approaches.

Plain Sew

The bag is sewn shut with no fold. This works with larger particle sizes that will not leak out between the stitches. Options include one thread, generally used with portable sewing machines, or two threads for fixed heads and high speed applications.

Plain Sew with Bag Top Fold Over

The top of the bag is folded before sewing. This reduces major leaking, which makes it a common choice for fine powders and small particle products. It costs a little extra time at the sewing head but saves product loss.

Tape Sew with an Easy-Open Pull Tape

A tape closure seals over the sewn seam, and an integrated pull tape lets the end user open the bag quickly without a knife. If your customers complain about cutting into product or about torn bags at receiving, this is worth the upcharge.

Whatever closure you choose, make sure your sewing thread and equipment match. Bag Supply Company supplies hand-held portable sewing machines, sewing thread for bag closure, and the related accessories through our packaging supplies line, so a closure problem does not turn into a second sourcing project.

Check 4: Filling Equipment Compatibility

A gross weight open mouth bagger operating under a control hopper is often the ideal setup for free-flowing products. Here is how the sequence typically runs:

1. An operator places an empty bag on a conveyor that transitions to the filling mechanism.
2. The bag mouth is presented manually or automatically on the fill spout.
3. The bag fills until it reaches the desired weight.
4. The filled, unclosed bag transfers to a sewing head, fed manually or automatically.
5. The closed bag moves to the pallet for shipping.

Every step in that chain is a place where a slightly wrong bag dimension causes a jam. Gusset depth, bag width, and mouth opening all have to match your spout and your sewing head. Before you commit to a production run, confirm the bag dimensions against the actual equipment on your floor, not the equipment in a spec sheet from five years ago.

Check 5: Barrier, Liner, and Moisture Protection

Paper alone is not a moisture barrier. If your product is hygroscopic, caking, or sensitive to humidity, you need either a coated structure or a separate liner. Polyethylene liners are a common answer, and they can be inserted as part of the bag construction or supplied separately.

This is also where food and ingredient buyers need to be precise. If your product is food grade, say so up front. Do not assume a standard industrial construction will satisfy your auditor.

Check 6: Printing and Brand Presentation

Multiwall paper bags are a large, flat, highly visible surface. For agricultural and building products that sit on a retail floor or a dealer shelf, print is not decoration, it is part of the sale.

Ask about print capability before you ask about price per thousand. Number of colors, coverage, and whether the artwork needs to be reworked for the bag dieline all affect lead time. A supplier who can produce the bag and print it under one roof removes a handoff where mistakes happen. Bag Supply Company runs solid printing and bag conversion capabilities at its Leeds, Alabama facility, which is one reason we can handle custom printed multiwall paper bags in pasted valve, sewn open mouth, and pinch bottom structures.

Check 7: Supplier Reliability and Stock Position

The best bag structure in the world does not help if it arrives three weeks late. Buyers should evaluate a supplier on four practical dimensions:

• Domestic production or warehousing: shorter lead times and no ocean freight variability.
• Quality systems: Bag Supply Company is ISO 9001:2015 certified, which means documented quality management rather than informal inspection.
• Breadth of supply: can they cover liners, thread, tape, and pallet protection on the same order?
• Program support: vendor managed inventory arrangements that keep stock on your floor without tying up your cash.

On the last point, our industrial packaging solutions page shows the markets we serve and how packaging requirements shift between feed, chemicals, agriculture, fertilizer, minerals, construction, food and ingredients, and seed.

Common Mistakes Buyers Make with SOM Bags

After enough orders, the same errors show up again and again.

• Buying on price per bag alone. A cheaper bag that leaks, tears, or jams the sewing head costs more than the savings.
• Ignoring the sewing head. Thread type and machine setup are part of the bag decision, not an afterthought.
• Skipping the drop test. Fill a few bags and drop them the way a pallet gets handled. The results are usually informative.
• Ordering custom print too late. Artwork approval adds time. Start it before you need bags, not after.
• Assuming one structure fits every product. A fertilizer line and a seed line rarely want the same bag.

How to Evaluate a Sample Before You Commit

Request samples in the actual structure you plan to buy, then run them on your real equipment with your real product. Check for seam integrity, bottom closure strength, gusset performance at the fill spout, and how the bag behaves after sewing. Weigh a filled bag and confirm it matches your target. Then palletize a full layer and move it with a forklift. Most problems surface in that last step.

If you want a reference point for what a properly specified multiwall bag looks like, our products page lays out the multiwall paper bag styles we produce, including sewn open mouth, pinch bottom open mouth, and pasted valve constructions.

Where Bag Supply Company Fits

Bag Supply Company is a family-owned, full-service bag manufacturer serving North America from our facility in Leeds, Alabama. We manufacture multiwall paper bags domestically, including sewn open mouth, pinch bottom open mouth, and pasted valve structures, with printing and conversion under one roof. We also supply bulk bags (FIBCs), woven polypropylene bags, polyethylene packaging, and the closure and protection supplies that go with them, so you can consolidate packaging purchasing instead of managing five vendors.

If you are comparing structures or trying to solve a leaking or jamming problem on an existing line, the fastest path is a conversation about your fill weight, product, and equipment. Start with the Bag Supply Company products page, or reach out directly and we will help you specify the right sewn open mouth paper bag for your application.

Frequently asked questions

What is a sewn open mouth paper bag used for?

Sewn open mouth paper bags are used for dry, free-flowing products such as animal feed, rice, seed, fertilizer, minerals, chemicals, and building materials. They are compatible with both manual and fully automated filling equipment, which is why they remain one of the most common industrial paper bag styles.

How is a sewn open mouth bag closed?

The bag arrives with the bottom already closed by the bag supplier. After filling, the user sews the open end shut with one or two threads, or folds the bag top over before sewing to reduce leaking. Tape sew closures with an easy-open pull tape are also available for quick discharge.

What is the difference between kraft paper and extensible paper in multiwall bags?

Traditional kraft paper is made from short wood fiber and builds strength through basis weight, with limited stretch. Extensible paper is made from long wood fiber and builds strength through stretch and flexibility, absorbing energy instead of tearing, which is why it is often used in two-ply constructions.

How many plies should a sewn open mouth paper bag have?

Ply count depends on the product weight, density, and handling conditions. Kraft constructions commonly run three to four plies, while extensible constructions often achieve comparable performance with two plies. Your supplier should match the structure to your fill weight rather than defaulting to a standard count.

Can sewn open mouth paper bags be custom printed?

Yes. Custom printing is one of the main reasons buyers choose paper over plain alternatives, and multi-color printing is available on most multiwall constructions. Bag Supply Company produces custom printed multiwall paper bags at its Leeds, Alabama facility.