A duct includes an inner tube configured to have fluid flow through to be transported and an outer tube surrounding the inner tube. The outer tube defines, in its interior, a plurality of auxiliary channels, which extend in the longitudinal direction of the outer tube and are designed to contain or have a further auxiliary fluid flow through, which is configured to thermally interact with the fluid to be transported.

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.