Thermium

Thermium is a late-game refined resource used mainly for high-temperature industrial builds. It is notable for providing a very large overheat tolerance bonus to buildings it is used in: constructions made from Thermium gain +900 °C overheat temperature, which makes it one of the best materials for machines operating in extreme heat. This is especially valuable for setups such as Thermo Aquatuners running Super Coolant or for building a sour gas boiler.

Thermium is produced in the Molecular Forge from 5 kg Niobium + 95 kg Tungsten = 100 kg Thermium. It can also be obtained indirectly through conversion: the Metal Refinery turns Thermium into Niobium at a 1:1 mass ratio, and the Rock Crusher converts 100 kg Thermium into 50 kg Niobium and 50 kg Sand. Because the Metal Refinery recipe effectively yields Niobium from Thermium with no loss in the Thermium portion, a small amount of Niobium can be used to “prime” the production chain after one or two trips to a Niobium-bearing asteroid, then expanded through Tungsten processing.

When melted, Thermium becomes Liquid Niobium and Tungsten in a 5% / 95% mass split. This makes it unusual among endgame materials, since it can be broken back into more basic components rather than simply becoming a single liquid form. Its melting behavior is also relevant in heat-heavy machinery and material handling systems that involve extreme temperatures.

Thermium is widely associated with the toughest late-game thermal engineering tasks because of its high overheat cap and the environments where it is practical. In particular, it is a strong choice for:

• Thermo Aquatuners that must survive severe heat loads
• sour gas boiler construction
• buildings placed in very hot areas where ordinary materials would fail

A few practical notes follow from its recipes and properties:

• Thermium is most useful once Tungsten and Niobium supply chains are established, since it is built from those materials and is not an early-game resource.
• The Metal Refinery and Rock Crusher can both be used to recover value from Thermium, but their outputs differ, so the choice of method depends on whether Niobium or Sand is more useful.
• Its main advantage is not raw material efficiency, but thermal resilience; players generally use it when the building would otherwise overheat long before the system itself becomes viable.

Overall, Thermium is a specialized endgame construction material defined by its exceptional overheat resistance and its role in the most demanding heat-management builds in Oxygen Not Included.