Nether is a dark, cold, physical substance naturally somewhere between liquid and gas. It has been found to naturally consume light and heat, and is destructive to nearly all types of matter, rather like an extremely powerful acid. However, it has a natural reaction to ferrous materials (iron, steel, celestium) that causes it to disperse. It is also very susceptible to thaumaturgic light, which burns it away extremely effectively. Fire and other sources of extreme heat are also quite effective at burning away nether.