If you've ever seen or used a Speck CandyShell, the two materials used in the Apple Bumpers are almost identical to those. The outside center of the Bumper is like the harder of the two compounds used in the CandyShell (a smooth, firm plastic), and the edges of the Bumper that form the lip around the front and back glass are like the rubbery compound of the inside of the CandyShell. This softer rubber is also the inside lining of the Bumper that actually comes in contact with the phone's antenna. Essentially it's like a CandyShell for just the outside edges of your phone. That's the best and most accurate way I can describe it.
I know what you mean about the "grippy" stuff. It's a pain in the butt to slide in/out of your pocket, & it attracts so much lint/dust. I don't see that happening with the bumper.
