i do poly for all baby gifts...you never know who's allergic to what and poly is hypoallergenic AND washes and dries during the length of one nap....(seriously, my kids watched the dryer till their 'blankies' were done)... i do cotton for wallhangings, hangs flat against the wall beautifully....BUT, for bed quilts ...i sandwich the backing, cotton, thinnest possible poly and then top... poly fills the quilting stitches and that's important to me... I have not used wool yet, but everyone i know who has says it's just dreamy... and the perfect thing for hand quilting, which i do on occasion...