I sure like cotton/natural everything, but if the spool of thread matches and it's poly, I'll use it. I like to use things that I have. Then I can buy more natural stuff! My machine loves cotton thread too. She can get a little uppity with the poly thread, but it still works out. I'd hate to discourage anyone from using what they already have. It usually works out fine and you're not wasting. When you run out buy what you can afford. Quilting is such a fun hobby, but it doesn't have to be so expensive.