If I remember right, the one of mine in the image below has a piece of inner tube on it, it came that way when I bought it here used. I also have another one and I put a Shur-Grip on it from 3rivers, but it's essentially the same material. It helps in colder weather as the aluminum riser can get very cold.
A word of warning: they're a real pain to get on, so be sure to have some pocket change ready for donations to the Swear Jar.
3rivers has a 'how-to' video for the Shur-Grip that is definitely worth watching.