This mat is too flexible for a medium pile carpet. In 22 years of working from my home office these are probably the worst chair mats I've ever purchased. It remains to be seen how long they last but I'm not optimistic. Would probably be more suited for use on a low pile carpet.
The carpet chair mat is not suited for over a carpet. I purchased the high pile style at least that is what the ad stated. I don't have a thick carpet at all and thought it would be fine. I set it on the floor and placed a five footed light weight chair on top. Without any additional weight in the chair the rollers made indention's in the mat. When you sit on the chair for just a short time the mat is so soft that the chair rollers sink into it and you cannot move the chair. The mat is not only not ridged enough but not thick enough either. It is not as advertised. It now sits on my porch awaiting return. It does not appear that I can give it less than one star or I would.