An eight-inch thick AAC wall has a static R-value of about 11. The real advantage is the dynamic R-value characteristics of ACC. The sheer mass of AAC combined with the cellular structure slows the flow of heat through the wall. By the time the heat absorbed during the peak summer daily temperature, moves through the wall, the exterior temperature has fallen and heat can radiate back out instead of continuing to move inwards. http://www.safecrete.com/aac/benefits/energyeff.cfm
The airtight nature of AAC reduces energy losses due to air infiltration. At the same time, AAC is ever so slowly breathing molecule by molecule. This characteristic works much like a Gore-Tex jacket, allowing moisture to pass out of the wall.