Ooya stone is unique and has all the softness of soil. The softest, brownest part of the stone, known as "miso", is the product of soil remaining inside the stone. It is a particularly porous stone because it is full of holes.
To come up with an advanced technique for using this material, Kengo Kuma and a team of engineers researched a diagonal form of construction consisting of a steel basket attached to a rod of the same material. This ensured that stone would not be simply a cladding material but contribute to creation of the building's structural skeleton.