Not really stiff and thick enough for a normal mid-thickness pile carpet. Might be OK on berber or really short pile. If you have a mid to thick pile carpet get the thicker one. Better than the thinner ones but still not enough.
Regardless of where you look the selection of chair mats for hard floors is very limited. Nonetheless this model is good for the price. Admittedly a rectangular (no tongue) model would be more preferred. However I found cost goes up substantially with size and shape. This is good for average sized rolling office chair.