I'm a 230 lbs person and I have not had any problems with my office chair sinking into the mat on old carpet (3/16" of pile left). I have been impressed with the stiffness of the mat but not the cleats on the bottom as this mat still moves about an inch each week after 40+ hours of use. Hence the 4 stars.
Mat works great for my husbands home office. The carpet was getting ruined from the wheels on the chair. Mat is sturdy and stays in place. Shipping was fast. What was strange was the mat didn’t come in a box so it was scratched in places and it had a big permanent marker X on it. I was able to get the X off with hairspray but next time Staples at least put plastic around it or in a box.