the invention relates to a method of closing an access side of a flexible packaging using a planar closure made of plastic , the closure comprising a slot delimited by limb parts and extending between the circumference of the closure and an opening , said method comprising the step of introducing the access side of the flexible packaging into the opening of the closure and the method comprising a subsequent step in which the slot is at least partially sealed by means of a seal , which connects the limb parts to one another , without substantially deforming the closure .