Diaper flannel is narrower, woven more tightly and generally only available in white. It is also double napped (brushed on both sides) for greater absorbency. Cheap flannel is sometimes only single napped, and you can see the criss cross woven fibers when you look at the surface. It will pill up after only a couple washes as the loose fibers twist around each other. Better quality flannel will have enough weight and bulk to it that the surface appears uniformly fluffy and it will last longer. Quilter's flannel is thicker, softer, comes in colors/prints and doesn't pill nearly as much. It is about twice the price of standard flannel, but worth it, IMHO.