Lightweight concrete weighs substantially less than concrete made with gravel or crushed stone aggregates. Generally the term is applied to concrete weighing 120 pounds per cubic foot or less and weights can range on down to 12 or 15 pounds per cubic foot. Such concretes are often used as thermal and sound insulation even though their compressive strengths may sometimes be as low as 5 psi. The lighter weight concretes 50 pounds per cubic foot or less which are the most effective as insulation, can be used in combination with other materials in wall, roof, and floor systems where they are the most advantageous in reducing heating and cooling costs.

These include: Perlite Concrete (a type of lava mined in large open pits in the Western United States, then crushed to sand-sized particles and expanded by heating); Vermiculite Concrete (a soft, laminated, mica-like mineral that when heated and flaked becomes a lightweight aggregate of great value for fill and insulating concrete); Expanded Polystyrene Bead Concrete (expanded polystyrene processed to a nominal density of 1 pound per cubic foot used as aggregate in lightweight insulating concrete); and Cellular Insulating Lightweight Concrete (which has a multitude of macroscopic, discrete air cells uniformly distributed throughout the mix that may account for up to 80 percent of the total volume).

Within the range of available lightweight concretes, the lightest ones generally offer the best insulating properties, but little strength. The user must consider not only the insulating value of the concrete but how it will be combined with other construction materials.