Method of manufacturing a filled packaging container comprising the steps of forming a bag on a mandrel, connecting a seam provided in a formed bag, forming a hole on an upper side of the bag and inserting a valve into the hole to provide an air pressure release after filling the container with a material. Two opposite edges of the valve are formed with two flexible portions made of foil. A sealing fluid is applied in the channel to provide a fluid film to connect the foil portions.