Precipitated silica is mixed with a fly ash material and is employed as an insulating material having a low thermal conductivity. The mixture of precipitated silica and fly ash material is dried, compressed, placed in an evacuable pouch, and evacuated. The resulting board-like insulation configuration is used directly as insulation. The board-like material which is produced may be used as insulation in household refrigerators and freezers by placing it in an insulation space between the inner liner and the outer case and encapsulating the board-like material with a foamed insulating material.