The chair mat that I purchased was for 1/4 inch carpet. It is simply too thin and the chair wheels create a divot that you can only get out of by rocking the chair until it moves out of the divot. I am not a heavy person at 175 pounds.
I purchased this item as a replacement for an older worn out model. Unfortunately it's not holding up. It's thickness does not hold the weight of the chair with a person in it without dimpling. I think it needs to be thicker to do it's job.
Although it's easier for my chair to roll across the carpet this mat could be thicker because the chair wheels make dents in it and get stuck. The chair mat also shifts and doesn't stay in place.