Purchased this last month and placed on top of what I consider 'normal' residential carpet (non-berber carpet). This chair mat is not thick enough plastic to support my office chair. After just a few minutes of sitting the chair's wheels create 'divots' in the plastic mat and after a few hours creates a memory of where my chair was. Spend the extra $ and get a thicker mat if you are going to place on top of non-berber (low profile) carpet.
This is the second chair mat I've bought from Staples at this price point for use on medium-depth household carpet. The previous mat lasted just three years before cracking badly enough to be unusable. This mat is clearer and looks thinner but after several it seems to be holding up better. My rolling chair hasn't worn any grooves into it. I wish it were a heavier more durable plastic but am hopeful that it will last longer. Note to other buyers: if you buy this mat rolled up let it warm and soften for about a day before trying to unroll it. Once you get it unrolled with the smooth side upward let it relax for another day. It will flatten fully but it takes a little patience.
I bought it in person and really like the price but it was too flimsy for the carpet. My chair and weight made big indents into the mat and hard to roll my chair around. It would flatten on its own. If I didn't have carpet. It would probably work better. I returned it.