A covering device covers a front area of a device for the passage of air. The device for the passage of air fits in an opening in a wall of a casing, in particular a casing of waste heat producing components, of an electronic cupboard, or of a switch cupboard. The covering device also covers a filter mat of the device for the passage of air. The covering device includes a cover covering the filter mat with a number of inclined lamellar elements, each lamellar element has in its upper area a section with a hook-type configuration orientated against the air admission.