If the fabric was polyester, I doubt if it needed to be ironed. Only iron if a piece of fabric is really wrinkled.
The test for yarn if it is wool or polyester, is to set a piece in a fireproof dish and light it, if the fire goes out,it is wool and if it is orlon, acrylic, polyester or synthetic anything, it will burn up and disappear. Synthetic fabrics and yarn are an oil by product. I haven't tried burning a piece of cotton fabric or yarn but my guess would be it would burn slowly. I think I will try it and find out.
Carol J.