A method and apparatus for manufacturing a double bag (20) are disclosed. The method comprises placing an inner bag (30) in an outer bag (40) through an open top end (42), inserting a gas feeding tube (50) between through the open top end (42), feeding a head space (44) between the inner bag (30) and the outer bag (40) with an inert gas through the gas feeding tube (50), extracting the gas feeding tube (50), and sealing the top end (42). A gas box (80) surrounds the open top end (42) to reduce the risk of oxygen entering the head space (44).