My .02 I do not like working with cotton poly blends when piecing. As a previous poster wrote, cotton is more forgiving and can be eased in or streched into place. I can not be bothered with adjusting my iron down to a lower temp when mixing a blend with 100% and in my early days did end up "glazing" (putting a shine and almost melting) the blend when piecing. Poly blends do not take a crease as easily when pressing and often fight me. I quilt because I enjoy the process but don't like working with blends so I avoid them. I do however love poly threads and battings.