Yes, I have used 80/20 and normal poly batting scraps for donation placemats. One guild I belonged to, made placemats for meal on wheels--one side Christmas and the other a non Christmas print. They would donate over 100 per year. I don't know about flannelette--even two layers. However, I prefer something heavier--more like you would use in a wall hanging, say.
In my search, I came across a reference to 'Pellon 75' but, unless I order it online, I can't actually 'feel' its weight.