Abstract: Method of making a sandwich lightweight construction material in which double fabric constituting the two sides of the construction material is made from fibers or yarns which consist of at least one polymer consolidating under heat, and pile threads forming the core material in the double fabric are interposed between and connected to the two sides of the construction material. The double fabric may comprise high-temperature-resistant polymer, and may further comprise inorganic fibers or yarns. The double fabric may be pretempered at temperatures below the glass transition temperature of the amorphous material of the polymer. The double fabric is thereafter subject to a heat or temperature treatment so that the fabric consolidates. The sandwich lightweight construction material made according to the disclosure can be used in all cases where low weight and high mechanical stability are important, particularly in aircraft construction.