The closure is the part of the specification most often left blank, and the part most likely to be incompatible with your filling line. A plain-language tour of the options.
Buyers usually specify size, material and print, then leave the closure to the supplier. It is worth two minutes of thought, because a closure that does not match your filling equipment will cost you throughput on every shift.
Sewn open mouth
The most familiar format. The bag arrives open at the top, is filled, and is stitched closed on your line. It is simple, forgiving on fill weight, and works with a wide range of products.
It needs a sewing head at the end of your line, and it is not the fastest option at high speed.
Valve bags — pasted and sewn
A valve bag is closed on all sides except a small opening in one corner. It is filled through that valve, and the valve closes under the pressure of the contents.
Both pasted valve and sewn valve formats are available. Valve bags suit fine powders and high-speed automated filling — cement being the obvious example — because there is no separate closing step after filling.
Pasted and pinched formats
Pasted open mouth, pinched bottom open mouth and self-opening square bags all use adhesive rather than stitching to form the bag. They give a flatter, squarer pack that stacks and palletises tidily, and they present a cleaner face for print.
Self-opening square bags in particular speed up manual filling, because the bag holds itself open.
Back seam and centre sealed
In BOPP and paper-laminated ranges, the back-seam or centre-sealed construction puts the join on the reverse of the bag. Two consequences: the front becomes an uninterrupted print area, and the bag holds a consistent size.
That consistency is the reason back seam is the most popular BOPP style — automated packaging equipment is far less tolerant of dimensional variation than a person is.
What to tell your supplier
Name the filling equipment if you can, or describe it: automated or manual, fill weight, and whether you have a sewing head or a heat sealer at the end of the line. That single sentence removes most of the guesswork from a quotation.
