User blog comment:Fedora Lord Para 348/Ask ParaGoomba!/@comment-24.99.118.30-20150220131836/@comment-1058260-20150220165445

There's no rust on the endoskeletons when they're visible, so it's not steel. Aluminum is a better assumption than titanium--the former is strong enough for an endoskeleton, far less expensive, and way more common a construction material.