A short while back there was a short discussion regarding "Hide It" (a permanent topping to keep the background from showing through on the embroidery}. At that time it appeared to be discontinued from Sew for Less. However, today I found it under the name "Stabilize It" at Amazing Designs. The price is outrageous a 26" x 36" piece for $8 per each color. I much preferred the 8 1/2 x 11 box of assorted colors. But when nothing else will work, I guess it's worth it.

You can get the Cover-Up Topping at the Hoop It All website.
Under Stabilizers.
It is the same as Hide It.
They sell it in various sized rolls or in pre cut sized sheets in packages of different colors.
Link below
Click on Cover Up.

I agree with pennyhal, too pricey for me. I use something called Cloud Cover from DBS. You iron it on the back of items that will be next to the skin, so sensitive skin is not scratched by the embroidery.

Yep. Too $$$. It would have to be something really really special to be working on to use it.