Plastic Piece for My Chair

I need to get to the store and get a piece of plastic to put under my chair here at the computer before I completely wear through the rug. I just noticed it is beginning to show signs of wear from rolling back and forth. I have two chairs that I use and both seem to be doing the same thing. I guess they are easy to find at Wal-Mart or Target so I will be going there the middle of the week and get one. It will be lots easier to move about too by the computer.