I made a batch of these for the Doncaster show, they are approx 15" square and consist of a layer of outer polar fleece, TWO inner layers of polar fleece, and another outer fleece layer.  

There is no waterproofing in these liners.  Great for show cages and also a good size to cover the front of the cages overnight.  There are 4 eyelets so you can hook them into place, or for rattie and chin owners, use them as hammocks or bumble pads.