Acoustic isolation for a hollow vehicle body part

The acoustic insulation assembly which is installed in a part (K) having a longitudinal direction and a tubular wall (1) comprises a section (13) able to be thermally expanded to form a foam. The section has two principal parallel faces extending along a principal plane from a first wall portion (1i) in the direction of the diametrically opposite wall portion. A section support comprises a retaining clamp before expansion coupled to a fixing clip (12) on the first wall portion. An Independent claim is included for a tubular bodywork part fitted with the acoustic insulation.