I use a match to burn a small piece of fabric inside an aluminum pie plate. If the residue is hard, then it is synthetic. If it is ashy, it is organic. Once I bought some gorgeous fabric in a clear plastic bag at a garage sale. When I pulled it out, it looked like a silky polyester. I used the burn test and it turned out to be silk! It had a cute lime green/pink daises and I made a short nightshirt and a matching robe. It washes and dries like a dream. Great for traveling, too.