Insulating panel for roof coverings

An insulating panel comprising a core layer of a synthetic foam material bonded adhesively on its topside to a sealing thermoplastic layer or sheet throughout the surface area of the topside for the covering of roof structures, said core layer comprising at least two superimposed foam sheets of an elastic, closed-cell crosslinked polyolefin foam material, said sheets being bonded together throughout the contacting surface areas by flame laminating, the bonding surfaces of the foam, initially melted by the flame laminating, together constituting a homogeneous polyolefin layer.