Steel

Steel is a refined metal and one of the most important late-game construction materials in Oxygen Not Included. It is primarily valued for its large overheat temperature bonus, which makes it the default choice for machinery and utility buildings that need to survive in very hot environments such as the Oil Biome and Space Biome. Because it is also accepted by buildings that normally require either Metal Ore or Refined Metal, it is a versatile upgrade material for many constructions.

As a building material, Steel increases a building’s overheat temperature by 200 °C. This makes it especially useful for high-heat infrastructure, including equipment that would otherwise be at risk of damage or shutdown. It is also required for several important endgame constructions and special recipes:

• Bunker Door: 500 kg Steel per door
• Bunker Tile: 100 kg Steel per tile
• All Rocket buildings, including the Gantry
• All parts of the Great Monument
• Serum Vial: 1 kg Steel + 1 Sun Nymph Egg
• Jet Suit: 200 kg Steel + 25 kg Petroleum

Steel can be produced at the Metal Refinery once Iron, Refined Carbon, or Lime has been discovered. The recipe consumes 70 kg Iron, 20 kg Refined Carbon, and 10 kg Lime to produce 100 kg Steel, and requires a Duplicant to operate the refinery. Since Iron and Refined Carbon can often be mass-produced while Lime may become the limiting ingredient, Steel production is frequently constrained by Lime availability rather than the other inputs.

In practical play, Steel is the standard material for anything that must function reliably under extreme heat or in space. It is commonly used for oil-processing infrastructure, high-temperature automation, and other advanced buildings where ordinary metals would overheat too quickly. Its role in Bunker Doors and Bunker Tiles also makes it essential for protecting the colony from Meteor Showers in space.

Steel is also relevant to a few specialized crafting chains. In the Apothecary, it is one of the ingredients used to make Serum Vials, and it can be used in Jet Suit production as well. Because of these uses, Steel is not only a durability upgrade but also a key resource in late-game logistics, space access, and advanced colony support.