The mat may prove to be too soft/too thin because depressions are forming where my chair usually is positioned. I've had it only for a week so it's too soon to tell whether it will discolor.
The strong "chemical" smell nearly cost this product its 5 star rating -- After three days in a well ventilated storeroom it "earned" its way back into my office. A great carpet protector despite my 220 lb body weight.
It's perfect for the Berber carpet we have. The indentations left by chair wheels disappear after a while (how long will that last?). The lip is just a little too short for under the desk.