It's a "balloon" made of Dyneema ultra-high-molecular-weight polyethylene fiber. They inflate it to 30psi and it has fantastic rigidity.
They had navigation difficulties but when they crashed it, it just bounced off the ground with no flexing at all.
The strength is obvious from physical size - everybody knows what 30psi does because that's a car tire.
Compare that to carbon fiber which shatters every time it hits the ground, it's just a game changer.
