There's been many a discussion on these boards about cotton vs polyester thread for use in both piecing and quilting. The general verdict was: it doesn't matter. In fact, this video explains why (and is often posted here when the question is asked):
http://www.superiorthreads.com/video...yester-thread/
So why then do even the newer quilting books - like Quilter's Academy which I've just started working my way through - still insist on cotton thread? There's an entire section about threads, where weight and ply are discussed, and then the authors end with "Be sure that you always use 100% cotton thread in your quilts"! Add to that the fact that in the machine quilting book by the same author (Harriet Hargrave) she encourages the use of nylon (invisible) thread to quilt, why the need for cotton for the piecing? I just don't get this perpetuation of the "100% cotton thread" myth.