Is burning the only test? The only way to tell the diff? I have prob 50 lengths (2 yd or more) of fabrics to "test". I can tell some have poly in them as they are very thin and stretchy, but some...even tho stretchy, they are thicker and even tho thicker...they stretch. I dont' want to use Poly in quilts...I have learned the hard way that it just doesn't work...but...I don't want to waste any fabric either! Any other suggestions?