Polymers

can be naturally obtained from obsidian scattered on the Martian surface and, once colonists have settled, can also be synthesized in Polymer Factories. It is mainly used for the construction of power accumulators, Domes and Spires.

Background
Some of the most important and widely used materials on Earth are made from polymers. While the dependency on such materials on Mars is artificially circumvented as much as possible due to the scarcity of the molecule (unlike Earth, Mars has no fossil fuel reserves to act as a polymer source), their importance cannot be avoided all together. Plastics, rubbers and more advanced isolations have a fundamental role to play in creating and maintaining pressure differentials between habitats and external areas.