Designers, builders and owners must become aware of the energy-saving potential of lightweight concrete used as insulating fill for floors and roofs. Lightweight concrete comes in an almost infinite variety of mixes and a wide range of densities. Perlite concrete, vermiculite concrete, expanded polystyrene bead concrete and cellular concrete have subtle differences. Cost and availability must also be considered. But each type of insulating concrete, if mixed properly with high-quality materials, and placed and finished properly, will do an excellent job.