A method for manufacturing a bag for use in vacuum packaging comprises forming a first panel having a receiving feature and a second panel having an insertion feature, such that the insertion feature can be removably connected with the receiving feature, thereby forming a zipper. Each panel comprises a gas-impermeable base layer and a heat-sealable inner layer molded from melt-extruded resin. The first panel is overlapped with the second panel, and three of four edges of the panels are heated such that the inner layers bond at the heated edges and the unbonded edge can be opened or closed via the zipper. Optionally, the bag can include a valve structure for evacuating the bag. This description is not intended to be a complete description of, or limit the scope of, the invention. Other features, aspects, and objects of the invention can be obtained from a review of the specification, the figures, and the claims.