An image featuring the pumice crete blocks used in the walls of this 200 square foot music and studio add-on we built just north of Santa Fe, New Mexico. This was our second time building with this material which has been documented and tested to provide good insulation. The blocks themselves were created by a small company south of Albuquerque and have the benefit of being light weight and stack able.
The result being the walls can be raised quickly with a minor amount of structural rebar added. Once the walls are stacked and reinforced the hollow cavities are filled with a pumice and cement slurry, which serves to fill them in. The theory is that it creates a pumice crete wall which does not need the extensive framing of the usual poured pumice crete wall system.
Given that pumice is a form of frothed volcanic rock and is abundant to some degree in the southwest, is has been used quite a bit as a highly insulative building material. It is the fluffed up, as it were, property of the pumice, which has air pockets hence insulation built in.