A sound damper for a fuel-cell system includes a tubular sound-damper casing made of plastic material. The casing is elongate in the direction of a sound-damper longitudinal axis. A first sound-damper end piece made of plastic material is fixed to the sound-damper casing at a first axial end of the sound-damper casing. A second sound-damper end piece made of plastic material is fixed to the sound-damper casing at a second axial end of the sound-damper casing. On at least one sound-damper end piece, at least one fastening element is provided for fastening the sound damper to a support structure.

A muffler for an exhaust system of an internal combustion engine includes at least one muffler component with a perforation defined by a plurality of through-flow openings in a wall of the muffler component. The through-flow openings can be flowed through in a flow direction in the direction from an upstream side of the wall to a downstream side of the wall. At least in the case of some or all of the through-flow openings of the perforation, a through-flow opening flow cross section decreases in the flow direction in order to provide a through-flow opening flow-guiding surface.