Abstract: A heat-insulating, fire-proof, water-resistant, permeable-to-air, flexible lightweight concrete with a volume-density below 500 kg/m3, made with polystyrene pearl is equally suitable for heat-, and sound-insulation of walls and slabs, as well as decreasing their water permeability or water-absorbing capacity, as well as increasing their resistance to fire at the same time keeping their ability to be permeable-to-air and humidity, for renovation old buildings or building new buildings. Its composition is: polystyrene pearl, or recycled polystyrene of 1-10 mm diameter, water, cement and organic (polymer) binding material mixed with cement: such homo-, co-, and terpolymers—which are water-soluble and/or can be dispersed in water. Resulting from the use of organic (polymer) binding material, the polystyrene pearls can easily mixed with the inorganic binding material and water. The heat-insulating material produced this way can be even 100 kg/m, depending on the quantity of the binding materials.