Abstract: A sound insulating panel is provided having a support layer of honeycomb material, and a pair of covering layers, at least one of which is air-permeable. The support, honeycomb layer has a compressive strength greater than the compressive strength of each of the covering layers, in a direction transverse to the faces thereof, and has a tensile strength which is lesser, in the general direction parallel to the faces, than that each of the covering layers. The support layer is compacted over a part of its extent to a substantially closed layer of reduced thickness, this being, preferably, in the region of the border. A method of making an insulating construction element as described.