i used YLI. it was very soft, BUT.... it messed up my tension and i had a bad time getting everything back where it belonged and every place it ended there where tiny pokeys that stuck out and itched even though i dragged it through the batting. it just worked it's way back out and itched like crazy. and that was the recommended brand for my machine. HAH! now, i would only use it for wallhangings or applique, where it sits on the surface. :evil: i don't know if it was poly or nylon.