Johnson,
Xenomorph,
11 years ago
I always believed that it was whatever matterial they had around them and they used their saliva like a glue epoxy coating to hold everything together. In some games, movies, and comics it looked like they had steel support beams trees and other items including corpses in the walls, saddly you had to actually look for these because they were rare.
And as for the original topic, I believe they made the cocoons out of the saliva after it hardened.