> Dirt is a very good insulator of both heat and sound Sound yes, heat not so much. While it can store heat due to it's thermal mass, it will release it quickl

> Dirt is a very good insulator of both heat and sound Sound yes, heat not so much. While it can store heat due to it's thermal mass, it will release it quickly due to a low R-value, depending on moisture content the R-value could be below 1 per inch. Cellulose has around 3.5 per inch. Without adding additional insulation to restrict thermal transfer, you need to build very thick walls. In sunny desert climates where days are hot and nights are cold, you can build your wall in a way that allows it to go through the heat exchange synced with the 24hr sun cycle, and then it's very efficient. Thinner cob walls need to be wrapped with insulation to slow down heat transfer.