A structural member including a lightweight core, one or more skins, and a crosslinking nanolayer interposed therebetween that results in significant mechanical strength in the structure. The core is a polymer of reduced density by way of included voids, such as an open or closed cell foam, honeycomb, or corrugated structure. The core polymer has a lower density and may have a higher softening or melting temperature than the polymer skin materials. The core may be discontinuous at the interface with the skin such that only a small percentage of the core surface is actually in contact with the skin compared to the overall area of the interface. The skin may be a thermoplastic layer that attaches to the core material. The skin may be a composite material including non-thermoplastic reinforcements. The crosslinking nanolayer is covalently bonded to the surface of the core material and provides molecular compatibility with the skin material.