Gusseting happens on the blown film line, typically just before or as the layflat tube passes through the collapsing frame. Folding boards or bars tuck each side of the tube inward, creating an inward pleat, or gusset, along both edges of the film. The result is a tube that, when it is later opened and filled, expands outward at the sides instead of staying a flat, two-dimensional pouch, giving the finished bag more volume and a sturdier, more box-like footprint.
Gusseted film is common in products like trash can liners, ice bags, and produce bags, where the bag needs to stand open or hold its shape when filled. The depth of the gusset, meaning how far the fold extends inward from each edge, is specified alongside layflat width and gauge, since it directly determines how much the bag will expand and how much material is used per bag.
Gusseting adds a mechanical step and a bit of complexity to the line setup, but it lets a single layflat tube become a far more functional finished package without any additional fabrication or seaming once it leaves the film line.
Glossary
Gusseting
A process of folding the sides of a blown film tube inward before winding, so the finished bag expands outward into a flat-bottomed or box-like shape.
Example
A liner converter ordering film for kitchen trash bags will typically specify gusset depth alongside layflat width and gauge, since the gusset depth determines how wide the bag opens once it's pulled over a can.
Nuance
It's easy to assume gusseting is purely cosmetic or a bag-making step done later, but it actually happens during film extrusion itself, before the roll is ever wound. Once a roll is wound without gussets, that geometry cannot be added downstream without re-running the film.