Desk-Chair Floor Mat?

Background: My home office area is carpeted, so many years ago I purchased, from Staples or Office Depot, a plastic floor mat, sold for this purpose, about 4' x 6', smooth on one side and with an array of sharp points on the other side. My desk-chair rolls on this very nicely, and the sharp points keep the mat where I want it on the carpet. Gradually depressions have developed in the mat, probably because the wheels of my desk-chair tend to rest mostly in the same place.
I'm looking for a way to get rid of these depressions, and for the mat to be flat again. My first (and so far, only) idea is to place it, smooth side down, on my concrete patio in the sun on a hot day - thinking that the heat might cause the mat to return to its original shape.
Any other ideas or experience out there dealing with this problem?
Thanks.
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CWLee
Former slayer of dragons; practice now limited to sacred
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I tried those plastic floor mats and found them lacking. I now use a piece of 3/4" thick 4' x 6' plywood for my desk chair to roll on. I nailed strips of 1" x 1/2" wood around the edges of the plywood to keep my chair from rolling onto the rug.
Been using the same piece for over 5 years and it will probably last for very many more.
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CWLee wrote:

That is probably the best and easiest thing to try. Those mats come in different grades and the thicker more expensive ones resist denting better. Also note that home carpets typically are much deeper pile than the commercial carpets these mats are intended to be used on so the mat is already over stressed. If the dents don't come out just buy another one.
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As Pete said those mats have different grades based on the flooring underneath. Staples actually has a chart in their catalogue for a better fit..
CP
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I doubt the sun will do much, but it will not cost anything to try i t. On the next mat, shift it around every month, just a few inches.
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