HOOGA Moveable Outdoor Fireplaces are built with heavy gauge Corten steel – also known as weathering steel because its unique alloy composition provides increased resistance to atmospheric corrosion. When left to weather outdoors, the surface develops a golden, rusty patina that seals and protects the steel underneath. The raw steel look of a new HOOGA will start to change quite quickly outdoors and should be fully rusted in 2-3 months.