User blog comment:SolZen321/What are UItras made of?/@comment-1698614-20131011100825

I believe the Ultras are in a sense organic, but they are made of a different form of matter than most beings, being light-oriented and all. They probably still have skin and all... except they bleed light, and can manipulate their energy for attacks.

I know that they are most likely not made of specium. Specium is a powerful element found on mars, according to the captain in the original show. In Ultraman Mebius, GUYS use Specium missiles for some of their machines. How Ultraman can use it so freely I do not know, but I doubt they're made of the stuff.