I use cotton and sometimes linen fabric almost exclusively, but use various threads, whatever is the right color or weight for the project. I do not life puffy quilts, so no high loft anything for me, and hate to touch poly - so warm & natural is my go to, although have no objection to bamboo, silk or wool if I find it at a price I'm willing to pay. I also haunt the thrift shops for good quality cotton sheets to use as fabric either for the top, or more typically for the back.