A structural element for use as a core layer in a sandwich composite element, wherein the structural element (2) is formed from a plurality of mutually welded body segments (4, 5) made from an extrusion foamed thermoplastic, and wherein the structural element (2) has a first face side (1) for bonding to a cover layer, wherein a surface of the first face side (1) that can be loaded with a resin (8) has open pores (6), wherein the surface of the first face side (1) is created by hot-element cutting, in such a manner that the surface is thermally sealed to some extent, wherein a gloss value of the surface of the first face side (1), measured at 60° in accordance with DIN 67530-1982 is between 2 and 10 gloss units.