A multilayered, sound-insulating, mechanically strong sandwich element comprising two facing layers (1) substantially attached to a plastic foam core consisting of at least two layers (2) which are joined through contact points (also called bridges) (3) creating a gap or gaps (4) between the core layers (2), and in case of long spans and/or thin facing layers, travel stops inside the gap/gaps (4) to keep the core layers (2) at a certain distance from each other, wherein the core layer material is a semi-rigid, cellular material containing more than 50 percent open cells, and has a tensile strength of more than 50kPa, and has a compressive strength from 5 to 200kPa, at 10 percent deformation. The distance between the contact points or bridges (3) is at least 350 mm. The new sandwich element can be used as a sound-insulating door, a partition element or a construction unit.