Due to the mathematical complexity of Gehry's design, he decided to work with an advanced software initially conceived for the aerospace industry, CATIA, to faithfully translate his concept to the structure and to help construction. For the outer skin of the building, the architect chose titanium after ruling out other materials and seeing the behavior of a titanium sample pinned outside his office. The finish of the approximately 33,000 extremely thin titanium sheets provides a rough and organic effect, adding to the material's color changes depending on the weather and light conditions. The other two materials used in the building, limestone and glass, harmonize perfectly, achieving an architectural design with a great visual impact that has now become a real icon of the city throughout the world.