All the materials! For structure – titanium. For form pieces – aluminum. For solar panels – Gallium arsenide. For electronics – glass, crystal, plastics! Diversity is the spice of life! Every part needs to be carefully thought through and the material selected should be the best one for the job.
Fun Fact: NASA has strict policies on what material you’re allowed to use. For example, there are types aluminium that NASA won’t let you use if you’re launching from Florida because the salt sea spray from the Atlantic might corrode it as it sits on the launch pad. The more you know!
The material which are light in weight so that they can be carried up easily defying gravity. In addition they are to be able to cope with high temperature. So the materials like aluminium and titanium are use to reduce weight and carbon and ceramics composite to cope with heat.