Gee, thinking of coasters - Darice makes 3-4 inch rounds and squares of plastic canvas - not expensive. Sewing scraps of batting on the canval and then covering with interesting fabric would be cute and you wouldn't be spanding time figuring out how to flatten the coasters after washing. I don't think I'd stick them in the dryer - too hot? but set them out on a towel to dry.
See:
http://www.everythingplasticcanvas.c...-mrl-c261.aspx
Jois