And one other thing blends do, as bearisgray discovered, they melt at lower temperatures than cottons. They can also have a tendency to "pill" on the surface if they are not good quality. I admit I do use blends quite often and have occasionally melted a patch or two that I wound up having to replace. And I do mix them with 100% cottons. I try to stay away from 100% polyester fabrics for all of the reasons listed above, but sometimes the perfect fabric contains polyester, so I use it anyway.