This is the second matt that I have purchased. I use it on a plush carpet and over time it breaks up. It does seem to discolor over time. I can't remember how long I have had the one I have now. It does make it possible to roll my chair on the carpet and saves the carpet from the chair.
I bought it to replace an inexpensive mat that I had for several years. This mat turned out to be lighter than my first one. I returned it the next day and paid quite a bit more for a better one.