Aerated concrete (aircrete) is manufactured using foaming agents or aluminium powder, as previously outlined in the section on foaming agents. Densities in the range 400–1600 kg/m2 give compressive strengths
ranging from 0.5 to 20 MPa. Drying shrinkages for the lowest-density materials are high (0.3%), but thermal conductivity may be as low as 0.1 W/m K, offering excellent thermal insulation properties. Factory autoclaved
aerated concrete blocks have greatly reduced drying shrinkages and enhanced compressive strength over site-cured concrete. Aerated concrete is generally frost resistant but should be rendered externally to prevent excessive water absorption. The material is easily worked on site, as it can be cut and nailed.