The invention can be defined in its most general form as a 3-D light core from sheet material, especially from 'NOMEX' polymeric paper, and can be used in production of sandwich panels as applied in aircraft production, construction and other branches of industry. With the aim to improve the core mechanical and unit weight properties, the paper base is perforated thereby increasing the base-binder bonding strength, whereof the binder is applied onto both sides of the base to increase its structure rigidity, owing to bonding of binder layers in-between at the locations of the holes. The quantity of the holes and their diameter are defined in a formula.