I was a bit surprised that as you sit in one spot the plastic or whatever the carpet is made from has a tendency to form a dent and does not allow moving around in the chair. I thought it would be more rigid and not become dented. However during the night it goes back to the smooth surface and is OK for a hour or two then becomes dented again and holds you in one spot.
Bought two of these two weeks ago. Put them on typical carpet and I bought the one that was recommended for this carpet (medium 3/8" to 3/4" pile). And they just don't stay still. I have to get up move my chair off them and move it back 2 or 3 times every day. Very annoying. Also when you sit in the same spot for a while they develop indents around the wheels and its actually a fair amount of effort to get get the chair out of them so that I can rotate around and get out of the chair. Not a happy customer here.