A packaging apparatus for forming a plurality of sealed packages filled with a pourable product comprising: - conveying means adapted to advance a web of packaging material along an advancement path; - an isolation chamber separating an inner environment containing a sterile gas from an outer environment; - a tube forming device being at least partially arranged within the isolation chamber and being adapted to form and longitudinally seal a tube from the, in use, advancing web of packaging material; wherein the conveying means are also adapted to advance the tube along a tube advancement path; - a delimiting element arranged, in use, within the tube and designed to divide the tube in a first space being in fluidic connection with the inner environment and a second space being arranged downstream of the first space along the tube advancement path, wherein the delimiting element is designed to provide, in use, at least one fluidic channel for fluidically connecting the second space with the first space and for allowing, in use, a leakage flow of sterile gas from the second space into the first space; - filling means adapted to direct, in use, a pourable product into the second space; - pressurizing means adapted to direct, in use, a flow of sterile gas into the second space for obtaining a gas pressure within the second space that is higher than a gas pressure within the first space; - a package forming unit adapted to form and transversally seal the packages from the, in use, advancing tube; the apparatus being characterized in that the pressurizing means are fluidically connected to the inner environment of the isolation chamber and are adapted to direct, in use, at least a portion of the sterile gas present in the inner environment into the second space of the tube. - conveying means adapted to advance a web of packaging material along an advancement path; - an isolation chamber separating an inner environment containing a sterile gas from an outer environment; - a tube forming device being at least partially arranged within the isolation chamber and being adapted to form and longitudinally seal a tube from the, in use, advancing web of packaging material; wherein the conveying means are also adapted to advance the tube along a tube advancement path; - a delimiting element arranged, in use, within the tube and designed to divide the tube in a first space being in fluidic connection with the inner environment and a second space being arranged downstream of the first space along the tube advancement path, wherein the delimiting element is designed to provide, in use, at least one fluidic channel for fluidically connecting the second space with the first space and for allowing, in use, a leakage flow of sterile gas from the second space into the first space; - filling means adapted to direct, in use, a pourable product into the second space; - pressurizing means adapted to direct, in use, a flow of sterile gas into the second space for obtaining a gas pressure within the second space that is higher than a gas pressure within the first space; - a package forming unit adapted to form and transversally seal the packages from the, in use, advancing tube;