There are videos of them building it. From what I remember, they rolled carbon fiber around a cylinder, making the flat part of the cylinder. Then they mated two titanium half spheres to the end of the carbon fibre cylinder. This was done using some kind of "glue". Meaning that the middle part had no titanium.

I think it was in Sub brief YouTube video. https://www.youtube.com/watch?v=4dka29FSZac&pp=ygUJc3ViIGJya...