Hexagon shaped Adhesive Backed Cork Square - size 3.25" from point to point. Make your own tile coasters. Simply peal off the white paper and center on your tile. These are made for 4" hexagon tile coasters. They have rounded corners to make it easier to peel off the paper. They come to me in a huge roll, so they will have a little cupping when you get them. Once they are stuck to your tile they will remain flat.
I believe cork backing is much better than felt backing for tile coasters.
-- Set of 24 -- 1/16" thick -- 3.25" from point to point