I use SoFine #50 in the top. I find no problems with piecing or quilting with a poly or poly blend. I often use Coats Duel Purpose for piecing and always for attaching binding by hand. On the long arm I prefer a poly, SoFine being my "go-to", but also Permacore and Glide. I carry some cones for people that think only cotton can be used--but most are #30 or 40 weight and linty.