A gusset is the section folded inwards at the side edges or the base of a bag. When the bag is empty it lies flat; when it is filled, the gusset opens out and gives the bag volume. This lets box-shaped or bulky products sit more comfortably in the bag.
Side gussets are formed during film production, while the bubble is being flattened. Bottom gussets can be made at the converting stage by folding and sealing. In a gusseted bag the seal seam passes through more than one layer of film, so the sealing settings are adjusted more carefully. The position of the gusset folds is also taken into account when planning the print; otherwise the print may look split when the bag is opened.