The Otter Box case isn't silicone itself. It's a hard plastic case. It has a silicone lining on the inside of the back that the n900 snuggles down into. The lining provides shock protection and keeps it a very snug fit. There is a frame for the front also that protrudes a bit so that when laying on its face, the touch screen held away from the surface by about 1/16 of an inch. One of the nice features of the Otter box is a silicon gasket around the kickstand in the back. The Otter box makes the back of the n900 flat (so it lies flat and still nicer than it does straight from the factory), and the gasket allows it to grip a slick surface and not slide around.

Overall, I have found the OtterBox to be an awesome improvement to the n900. However, I do have one problem with it. The frame for the front of the device feels a bit uncomfortable when you hold it like a phone against your ear. Other than that, I have no complaints