Back-Seal Bag
Also called: back-seal pouch, center-seal bag, fin-seal pouch
A back-seal bag is a flexible pouch defined by its single vertical center seal running down the back of the bag — the strip of welded film that closes the tube after the forming collar has wrapped it around the product. The back seal (also called a center seal, fin seal, or lap seal depending on overlap) is the structural signature of the format, and it is the workhorse of the global packaging industry.
In practice, the back-seal designation is the structural description beneath what most buyers call a pillow bag. Almost every VFFS-formed snack, coffee, rice or frozen-food pouch on a supermarket shelf carries a back seal. The distinction matters in B2B sourcing because it focuses attention on the seal itself — its placement, integrity, and appearance — rather than on the overall bag shape. A back seal can be hidden behind a printed pattern, left visible as a deliberate design feature, or specified as a fin seal (film folded outward with the inside facing out) versus a lap seal (film overlapped with the printed side out).
Because the format uses a single continuous web of film, back-seal pouches run on standard vertical form-fill-seal (VFFS) machinery at high speeds — typically 60 to 250 cycles per minute on commodity lines, and well beyond that on multi-lane snack configurations. That speed, combined with low film cost and universal machine compatibility, is why the back seal remains the default for high-volume dry products. The format shares the same limitations as pillow bags: it lies flat rather than standing on shelf, and it is not resealable without an add-on. Brands wanting shelf presence upgrade to gusseted or stand-up variants.
Specifications
| Common materials | OPP/CPP, OPP/PE, PET/PE |
| Width range | 60–250 mm |
| Length range | 100–400 mm |
| Filling range | 5–1000 g |
| Production method | VFFS |
Common applications
- ▸Snacks
- ▸Dry foods
- ▸Rice
- ▸Frozen vegetables
- ▸Coffee
- ▸Confectionery
- ▸Baked goods
- ▸Nuts & trail mixes
Pros & cons
Advantages
- ✓Universal VFFS format — virtually every forming-tube machine supports it
- ✓High throughput — single-web film run at 60–250+ cycles per minute
- ✓Wide material compatibility (OPP/CPP, OPP/PE, PET/PE and barrier structures)
Limitations
- ✗Same limitations as pillow — doesn't stand, no reseal without add-on
- ✗Generic appearance without gussets or premium print finishing
Machines that make this bag
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Frequently asked questions
What is a back-seal bag?
A back-seal bag is any flexible pouch whose defining seal is a vertical strip down the back of the bag — the center seal that closes the film tube after it has been wrapped around the product. The back seal is the structural foundation of most VFFS pillow-style pouches, distinguishing them from side-seal or four-side-seal formats.
Back-seal vs pillow — are they the same?
Closely related, but not identical. A pillow bag is a specific shape (flat, with crimped top and bottom seals and a back fin seal) and a back-seal bag refers more generally to the seal structure itself. In practice almost every pillow bag has a back seal — so in B2B sourcing the two terms are often used interchangeably to describe the same VFFS-formed pouch.
What machines produce back-seal bags?
Vertical Form-Fill-Seal (VFFS) machines are the standard platform — the forming collar wraps the film into a tube, the longitudinal seal bar closes the back fin seal, and cross-seal jaws crimp the top and bottom of each pouch. Almost every Lintyco VFFS in the BG series produces back-seal bags, with speeds from 40 to over 250 cycles per minute.
Back-seal vs side-seal — what's the difference?
A back-seal (center-seal or fin-seal) runs down the back of the pouch, leaving the front panel clean and uninterrupted for branding. A side-seal runs along one or both side edges — common in three-side-seal or four-side-seal premade pouches. Back-seal is the VFFS default; side-seal dominates HFFS premade-pouch formats like pharmaceutical sachets.