Filter device for an exhaust system of an internal combustion engine e.g. self-igniting internal combustion engine has filter bag which has filter element and frame element which carry filter element

Filter device has a filter structure with a filter bag whereby the filter bag is restricted by gas-permeable recess wall. Filter bag has a filter element (60) and a frame element (50) which carries the filter element and at least one filter element is flat. The frame element comprises edge areas (62) of the filter bag. Independent claims are also include for the following: (A) Filter structure of a filter device; (B) Filter bag of filter structure of filter device; and (C) Method for the operation of filter bag of the filter structure of filter device