A viscoelastic plastic interlayer to be incorporated between two glass sheets of a glazing provides it with vibro-acoustic damping properties. The interlayer includes two outer layers made of standard PVB, first and second inner layers made of viscoelastic plastic material based on polyvinyl acetal and plasticizer, with improved acoustic properties, a central layer made of standard PVB, the first and the second inner layers being arranged, respectively, between the central layer and the first and second outer layers. The viscoelastic plastic interlayer, when incorporated between two glass sheets to form a laminated glazing with vibro-acoustic damping properties, allows an improvement in the acoustic insulation properties, in particular within a frequency range of between 1000 Hz and 5000 Hz, in which range the human ear is the most sensitive.