A method of gas filling and sealing of a duct intended to be filled with gas and positioned in a container of a collapsible type, said duct being defined by two opposite side walls which are joined along a connecting portion, and comprising an inlet arranged through one of the side walls, the method comprising:
- clamping a part of the container, which part comprises said inlet, between an abutment and a gas module which is axially movable towards the abutment, in such a manner that one of the two side walls included in the duct is allowed, in response to a gas flow supplied from the gas module and entering the duct through said inlet, to bulge to form a free passage into the duct for filling the same with gas, the abutment is formed with a recess in its side facing the container to allow said bulge;
- and
- after completion of the gas filling, sealing the duct.