Beautiful quilt! I too am guilty of using polyester thread for my quilting, Coats and Clark Dual Duty XP to be exact. I always thought it was cotton covered poly but I looked at a spool the other day and it is 100% poly. I don't feel guilty at all! My mother always sewed with Coats and Clark and so did my Great Aunt who was my quilting inspiration. I'm not worried about my quilts not holding up!!