My fuel tray (burner) came with a white cloth inside it. What is this and should it be kept or thrown out?

The white cloth inside some fuel tray (burner) models is a nonflammable fiber that has shown to create a better dancing flame more evenly across the opening. It is not required to be used and you can still use your fireplace without it. However if you do use it, make sure it does not cover the small holes inside the top of the fuel tray as they are needed to supply oxygen to the fuel.