Sewn Open Mouth (SOM) Paper Sacks
Filled from the top through an open mouth, then closed with thread on a sewing line or with a tape closer. The simplest, most tolerant paper sack construction — and often the cheapest way to pack granules, seed, grain and irregular fill weights.
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When an open mouth sack beats a valve sack
Valve sacks are fast, but they demand consistent product flow and a matched filling machine. An open mouth sack accepts almost anything: granules, seed, pellets, flakes, mixed fill weights, blends. It is closed after filling by a sewing head or a tape closer, which most plants already have, and the tooling cost is lower because only the printing needs cylinders, not a valve patch.
It is also the easier construction to seal well against moisture: a sewn bottom and a sewn top give a closed tube, and any barrier ply you specify is continuous through it.
- 2 to 5 ply kraft paper, brown or bleached white
- Sewn bottom as standard; pasted bottom available
- Closed after filling by sewing or tape closer
- Tolerates varying fill weights and denser products
- Barrier plies: PE film, aluminium foil, PP lamination
- Flexo printing up to 6 colours
- Micro perforations for moisture release
Typical specification
| Plies | 2 to 5 ply from fill weight and product density |
|---|---|
| Bag capacity | 5kg to 50kg |
| Bottom | Sewn bottom (standard), pasted bottom on request |
| Top | Open mouth, closed by the customer with sewing or tape |
| Standard sizes | 5kg 300 × 500mm · 10kg 350 × 600mm · 25kg 450 × 750mm · 50kg 550 × 900mm · custom to your line |
| Paper | Virgin kraft, natural brown or bleached white, 70 to 90 gsm per ply |
| Printing | Flexo up to 6 colours |
| Packing | Palletised and stretch wrapped, or bales |
FAQ
What does my sewing line need to handle an SOM sack?
Nothing unusual — standard bag sewing heads handle kraft paper sacks well. Tell us your sewing head model and whether it is a single or double thread chain stitch, and we will set the top edge construction and the mouth stiffness to suit it.
Can an SOM sack hold 50kg safely?
Yes, with the right ply count and paper grammage. A 50kg sack of a dense product such as cement usually needs four plies; a 50kg bag of a lighter product such as feed may need three. We specify from the product, not from habit.
Can the sack be opened easily by the end user?
Yes. We can add a tear strip, an easy-open notch or a printed opening line so the end user opens the sack cleanly instead of cutting it open. Ask for it at the artwork stage.
Not sure whether you need SOM or valve?
Tell us what you pack and how you fill it. We will recommend the construction, and we will explain the cost difference between the two.
- Emailsales@unisunpack.com
- Tel / WhatsApp+86 15825665852
- FactoryWenzhou, Zhejiang Province, China 325000
- Response timeWithin 24 hours, Monday to Saturday
