Your spaceships are made of various modules of one ore more different materials – be sure to combine them in clever ways so that you get the advantages of every material. These are your choices:
Titan is your basic material. It is very sturdy but also quite heavy. Still the modules are worth research as they are the backbone of your technology.
Carbon is much lighter than Titan but the Carbon modules are more complex and costly. If you want hightech and maneuverability, Carbon is your choice.
The Bio modules are made of organic material. It is quite sturdy but at the same time fairly light. They also have another big advantage: they regenerate above planets so you hardly need to repair them.
The Litho modules are made of massive amounts of living rock – almost impenetrable, but they really make ships slow. However, while your hangar is restricted in size, weight is not a problem.
These are the factions that are available in the initial release, yet more are bound to follow…