1) Heat oven to 200 degrees F (~95 C).
2) Put the template into the oven foil side down and wait for the plastic to turn from white to clear (should take 5-10 minutes).
3) Take the template out and let it cool on a flat surface until its cool enough to touch.
4) As soon as it is cool enough to not burn you take off your shirt off, lie down on your stomach and have someone place it onto your back with the plastic side down (foil side facing the ceiling- use the line on the foil to line up with your spine and make sure the arrows on it are facing towards your head so I know which way is up when I get the mold back). Pulling your pants/underwear down your butt a couple inches so they aren't part of the mold is a good idea.
5) Have your helper gently push the mold into your back starting in the middle and working to the edges. I find it works best to keep one hand pushing down along the spine and to use the other hand to mold the sides from the spine out to the edges. Once the mold is shaped it must cool back to room temperature. An extra 5 minutes of patience here pays off, wait until it really is totally cool. A fan blowing on or putting a cold wet towel over it helps it cool down quickly if you are in a hurry.
6) You are done, mail it back and I'll get to work.