It have been my experience that cotton batting is usually a light cream color and poly batting is a white. Also, poly is usually put together so you can see little tiny openings in it. Cotton batting is more dense and usually thinner. You can usually pull poly apart without too much effort where you cannot do that with cotton. I believe that poly will melt quickly and cotton will mainly singe and burn. Hope this makes sense. My DH and I make miniature ironing boards and we always use insulbrite on the pressing surface as well as cotton batting. Hope this helps