I always see reviews talking about the dents made by an office chair on mats but I never experienced it myself. I bought an amazing tough mat a while back but needed to upgrade to a larger one. I received this at my doorstep and in no way was it flat. Which I wouldn't care about except for the fact that it is supposed to be flat because if it is this malleable then a chair would certainly dent it right? Yup. I'm only about 140pounds plus the chair of course and within 5 minutes of sitting in the chair on the mat there were definitely dents I could hardly "scooch" out of. Worse than a carpet.
While it serves the purpose the desk chair used on the mat makes grooves in the mat which means after continuous use it will be needed to be replaced after a small period of time.
As described by many others the chair mat is very thin and had to move on. You get what you pay for. Now that I've ended two sentences with prepositions I'd better quit.