A STRUCTUREAL LIGHT-WEIGHT PANEL OF HIGH STRENGTH, HAVING THERMAL INSULATION PROPERTIES THAT RENDER THE PANEL PARTICULARLY SUITABLE FOR CRYOGENIC AND ELEVATED TEMPERATURE APPLICATIONS. THE PANEL IS CONSTITUTED BY A COMPOSITE CORE BONDED TO A CARRIER MEMBRANE OR LAMINATED TO FACING SKINS, THE CORE INCLUDING AT LEAST ONE LAYER FORMED BY A SERIES OF BALSA BEAMS IN SPACED PARALLEL RELATION, THE SPACING BETWEEN THE BEAMS BEING FILLED WITH SLABS OF FOAM PLASTIC MATERIAL WHOSE K-FACTOR IS SIMILAR TO THAT OF BALSA, WHEREBY THE OVERALL THERMAL INSULATING CHARACTERISTICS OF THE COMPOSITE CORE ARE EFFECTIVELY EQUIVALENT TO THAT OF A HOMOGENEOUS CORE COMPOSED ENTIRELY OF FOAM PLASTIC MATERIAL, WHEREAS THE STRUCTURAL CHARACTERISTICS OF THE COMPOSITE CORE ARE FAR SUPERIOR THERETO.