I just received my der kaiser from continental. I can't believe how stiff the sidewall is!!! The casing around the bead of the tire is a stiffer harder rubber than the casing around the thread. It feels like a dual compression rate spring! When you ride this tire, you can run it so that the first part of the tire compresses very easily, but the end of the tire is harder to compress.
I am running 12psi in this tire now, and it feels basically the same stiffness as my maxxis minion dual ply with 18psi!
The rubber compound is also stupidly sticky. This is definitely my favorite tire.