The Second Alien War had a host of new alien technologies, that served as a major obstacle for the X-Com forces in the early days of the war. One of these new technologies was an alien alloy that combined extreme durability, impossibly light weight and incredible flexibility. These materials, called Aqua Plastics for their wide range of submarine combat applications, were the base for all alien weapons and vehicles. They are easily replicated and can be used to manufacture alien technologies as well as personal armor and X-Com/Alien hybrid technologies, like the Displacer hovertank to the mighty Leviathan submarine. However, like their counterparts from the First Alien War, they tend to fill up storage space rather quickly, but they do sell for a fair price when you decide to empty out the stores.