A lightweight metallic honeycomb core panel structure having a high strength, a highly contoured surface and possessing relatively low thermal conductivity through the panel is prepared by bonding a first adhesive sheet and a peel-ply cloth to one edge surface of a honeycomb core prior to contouring the core into the desired shape with the first sheet applied to the surface which becomes the convex side of the panel. Sufficient force is applied to the sheet in order to force the edge of the honeycomb core through the uncured adhesive and the sheet is bonded to the core forming a structural fillet. The core is then contoured to the desired shape with the peel-ply acting to prevent spreading of node bonds at the convex surface. A second sheet also comprising an uncured adhesive material and a peel ply cloth is bonded onto the second side of the core so that a fillet is formed on the core cell walls. The peel-ply cloths are then removed to expose a bondable surface. A layer of uncured adhesive sheet material is then applied to each surface of the core, and metallic face sheets applied thereon. The adhesive sheet is cured forming a honeycomb core panel having thermal insulation barrier between the core and face sheets provided by the second adhesive sheet.