The backbone of Dragon 2 is a metallic welded pressure vessel. SpaceX has completed manufacturing of the first two pressure vessels to be used for ground testing, and is currently manufacturing two Crew Dragon flight articles. The pressure vessel is the primary structure of the spacecraft that protects astronauts during ascent, while in outer space, and during entry and landing to provide a safe and controlled environment in which to travel and work.
Here is a picture of the first test article undergoing structural load testing. This demonstrates the spacecraft’s ability to withstand the tremendous forces it’s exposed to during space flight.
When we transport astronauts on Crew Dragon to the International Space Station next year, it will be within one of these pressure vessels that over the coming months will turn into a fully functional spacecraft.