The plastic sinks in when you sit in the chair for a while so it makes it so the chair does not roll easily which is the reason we bought the mat for:( No we are not big fat people!
The chair mat meets our needs but does have some short comings -- it moves on the carpet as the chair is moved and does get "dents" from the chair wheels making it hard to move the chair. This mat was for medium pile carpet -- I could not find a mat for longer pile carpet. This one is definitely better than many other mats out there. This mat was delivered flat to our front porch -- much much better than being rolled up in a box. The mat has laid flat from the time it was delivered -- a definite plus for this product.
We have the typical medium pile home carpet and this does not work at all It deforms to the point there's no way the chair will roll. Worse yet the deformity is basically permanent so there's no way you can move to a new position. This MIGHT work for very short pile with no carpet pad that you would find in a business or professional office setting.