I use vintage thread, but good brands on my Janome 10000 that I find in yard sales and at auctions. Most are cotton wrapped polyester. Some are 100% cotton. I am not a purist, and have a limited budget so being frugal is important to me. I test 100% cotton thread, by wrapping a length around my fingers (like I do for flossing my teeth), and give a yank. If the thread breaks very easily, I don't buy it or use it. The quilter's that came before us, used what was available, today some quilter's are true purist. That is not me.