I spent the extra money to get a quality floor mat for my office a medium pile carpet. The first time I sat in my chair on the mat it made serious indentations. The mat does not stay in place. Would not recommend to anyone.
Potential buyers should know that this mat while very good is somewhat thin and therefore subject to indentations from the wheels. This is most likely if you use it on a thick carpet. On a hard floor I doubt that it would matter.
After one hour this mat already had permanent dents from my chair's rollers. Now the chair's tendency is to roll into those spots I can't scoot forward. If I need slide around to get something near my desk I can but the chair goes back to the same position. It's my fault for trying to get away with buying a cheap one. In case you're wondering I'm only 165 lbs. the mat needs to bear that kind of weight. Very disappointed.
It took several days to flatten out even after flipping it upside down and back again. It is not hard enough to prevent imprinting chair casters after seated in chair. It might be best for hard floor or very low carpet but too soft for anything above 1/2" carpet and pad. Best thing to say reasonable price and chair moves easily before impressions set in.