I prewash because of what the chemicals on the fabric do to my finger tips and nails. I recently bought a kit with 9 pieces of 1/3 yard cuts - all 9 shrank. It was the first time that ever happened to me, but it was probably because I didn't put them in the mesh bags. But better to shrink before than after. I had to adapt the quilt, which was not a big deal but I was surprised. Also, I could have dried them on a clothes rack but that didn't occur to me. When I wash my jelly rolls or charm packs I don't put them through the dryer, they are either flat dried or hung on a clothes rack. My reason is to remove the harsh chemicals.