It's a Silicone Dog Dish Mat from Amazon (
LINK HERE). It's real easy to clean up. I got the 19 x 12 size. If I had it to do over I'd get the next size larger (24 x 16). I lined the bottom with a piece of perforated shelf liner from the home center. Any water drains through so there's not a puddle. After this photo was taken I got inexpensive stone holders for my three stones (
LINK). They stay put like they're glued to the mat but are easy to reverse or move to the side for whatever reason. The thing I like best about the setup is that I can carry the kit in whole or in part to the sink and clean it all up periodically.