here's what my sister, the "Embroidery Queen" (seriously!) would say: yes, just a cheap muslin behind the blocks for hiding any thread tails under the fabric. Also, be sure to cut your blocks a little bigger so that it accounts for the drawing up of the fabric when you embroider. She also does not use a hoop--says she can get smaller stitches that way and I have found that to be true too. Last thought--I do her quilting (almost all her quilts are embroidered) and I treat the blocks like applique--quilt around the design and a tighter fill in the background to make the embroidery really "pop". I often put extra wool or poly bat behind the embroidery blocks to help with that.