As described by many others the chair mat is very thin and had to move on. You get what you pay for. Now that I've ended two sentences with prepositions I'd better quit.
This mat was described as being appropriate for carpet pile up to 0.75-inch thick which should have been right for my rug that is only 0.4-inch thick. The prongs on the back of the mat are only about 1/8-inch long and consequently do not penetrate the carpet an adequate amount to keep the mat in place. The mat shifts constantly and I have to readjust it several times a day to keep it straight and under my desk. I do not recommend this mat for carpet with pile higher than 1/4-inch.