Device and method for sound damping device in cavities of vehicles

A sound damping unit (16) especially for use in vehicles, comprises a carrier material (4) and a shuttering material (2). The damping material forms an open cell structure, and has an absorption coefficient for sound in excess of 0.5. The shuttering and/or damping material are expandable, especially under heating, and direct contact between the damping material and the wall is avoided. The shuttering material is used to form a closed cell structure, and its water uptake is less than 10%, especially 5%. The process used for sound damping comprises fixing the material to a structural element, and then thermally expanding it.