The only reason for returning the matt was because it walked on my carpet. Although the carpet is not that plush it is dense and possibly has a high nylon content. I'm told that is why sometimes matts walk and sometimes they don't.
As soon as I put my desk chair (5 point ball casters) on the mat divots were created. I could not easily move the chair. I didn't even sit in the chair yet! This does NOT work for medium to high pile carpet at all. The advertised use is completely bogus.