Any building material can have one or more of several characteristics:
Is it indigenous (common) to the area?
Does it provide thermal mass for insulation and heat conduction?
Is it durable or susceptible to rot?
Is it easy to work with or does it need specialized training to manipulate?
Most typical modern building materials will only satisfy one and perhaps two of those characteristics. There is not a single modern material used that satisfies all four characteristics. However, the materials used to produce the building blocks for the Earthship’s primary structure encompass all 4 aspects of the best building material: used tires.