User blog comment:DinoTaur/Welcome to Prof. Dino's Aurology Class!/@comment-25814498-20160218235631/@comment-17259909-20160220173423

Well, not all rubber properties. Just the ones that allow it to act as it did against Bopobo. I mean, it probably wasn't steel (unless he made it super flexible). The crux of my theory is that even as Nen, aura does not have any mass, but develops mass-like properties. It seems like it has mass, but in actuality, it has none. It's virtual mass, if you will. It causes what it interacts with to act the same way. And what makes Nen so powerful is that the user can choose which properties of mass their aura will take.