One of the most surprising qualities of aluminum is its strength-to-weight ratio. Most metals are heavy, buy aluminum has one-third the density of iron, copper, or zinc, and can be strengthened through alloying without changing its weight. This property makes aluminum the material of choice in aviation and architecture. Not only has it been used for airplane bodies, but it also can be found in interior furnishings and equipment. Architects and designers were freed from the constraints of heavier, more cumbersome materials, so design and materials could work together.