I have used this layering before for non-leaking coasters;
top layer - decorative cotton
inside - insulbright or regular thinner batthing
another Layer of scrap/extra cotton
then - clear plastic from joanns, I can't remember the thickness I purchased.
last/bottom - those waffle weave placemats cut to size or shelf liner for non-slipage.
I quilt the top three layers, {stabilizes the batting} add the bottom two layers and zig-zag, serge, or bind around the edge. You don't want to quilt the plastic layer and punchy holes in it {don't ask me how I figured this one out, LOL}.