The quilt I just finished on my DM has Isacord poly, Sulky rayon, C & C poly covered cotton, and Guterman poly in its FMQ. All worked fine and I'm sure will continue to do so. I was more concerned over color than content. When piecing, I use any of the Guterman poly in the bobbin to save space and either that or some of my stash of C & C for the top. Some Connecting Threads cotton, too, but it's a little linty. I've heard the new C & C poly covered poly isn't as good as the old - it stretches, but I haven't tried any yet. If the thread tests strong, I don't worry about it.