you don't need to if you are using ALL flannel and plan to wash it well after you are finished. If you are mixing it with cottons, then you can wash them. Soak in a sink of HOT water...then SPIN to damp in a salad spinner and press to finish...of course they will all shrink differently and you will have to make them all the same size again, but it works! You might also want to spray with starch and BLOCK them to make sure you are getting the FULL use of the fabric.