You actually want the pieces to not slide as that increases the risk of distortion.
I have mine covered with the silver stuff, but will be removing it when I find the cotton duck fabric that I have stashed somewhere. Aside from being slipperier, it doesn't allow the fabric to dry as easily when you are steaming it.
Also - you don't want too much padding - the harder the board, the better the seams will press.
Cheers, K