A super awesome alloy. Much like titanium.

One of the central elements of Gundam Wing's mobile suits is the use of Gundanium Alloy. What makes Gundanium so incredible is its properties: it is practically immutable, highly heat-resistant, and electrically neutral. These properties combine to produce a material that is extremely hard to damage, lending to the Gundams' atmosphere of invincibility and intimidation. Additionally, heat and beam weapons produced using Gundanium are much stronger than similar weapons made using traditional titanium, thanks to its extremely high melting point allowing it to produce hotter and therefore stronger beam energy. The name is actually a misnomer, since Gundanium is not technically an alloy; it contains non-ferrous metals and non-metallic elements. Gundanium is very rare and hard to make, since it requires the use of super-heated plasma and nanomachines, and very few people know exactly how to make and refine it. Further, it is said that Gundanium can only be produced at Lagrange points under zero-gravity conditions, putting a very powerful tool in the hands of the colonial rebels.

There is a common misconception that Gundanium is nigh-invincible; this has been disproven by several instances in Gundam Wing and Endless Waltz where the Gundams were damaged, usually by beam weapons. However, this has also lead to the supposition that Gundanium is especially strong against solid weapons, like traditional machineguns (as is the similar alloy Gundarium, from the Universal Century). Th...