Product Guide Autoclaved Aerated Concrete The porous AAC structure comes from being “leavened” with aluminum. Photo: H+H UK Behind the recommendations Related articles Behind the recommendations Related articles Autoclaved Aerated Concrete Lighter, more fire-resistant, and a better insulator, autoclaved aerated concrete is a great alternative to regular CMUs. More about Autoclaved Aerated Concrete Autoclaved Aerated Concrete (AAC): Will the U.S. Ever Lighten Up?