If it is good quality polyester or cotton, either would be suitable to quilt with. However, I prefer good cotton on good cotton quilts as it is my belief that it goes through the material more smoothly than other fibres. It also washes and irons in much the same way and so you don't have to pay extra care because of the thread you have used. I use every weight from 12 to 60 on my quilts as I like decorating them. The only time I use the rayon is for embroidered sections, but not to quilt.