Well, there is not much design in it. I had a new copper 10 L boiler, that sat on a ring on the fire.
As it took much more energy than my previous boiler, I thought about some kind of insulation. Of course one could use blankets of glass wool or stone wool, but I have my stil in my kitchen and don't like glass wool in my food.
In a take away where I often come, I asked for two large 20 L oil cans. I took out the top lid of one of them, cleaned it from the oil and made a opening in the bottom to fit my boiler. Then I found a sale offer of a blanket to shield a car window from the cold,made of aluminium foil with some plastic layers inside for only EUR 2.50, so I wrapped that around the oil can.
The other can I used later: both of them today alongside each other on this picture.
(Sorry: on my own computer they are shown upright.)
My original idea was to capture the heat flowing upward alongside the boiler and so being lost.
It worked: as said I used 50 % less energy for a whole run. Saves me about EUR 0.35 each run!
Later I found another boiler and used the second can. The oil in it had dried and I tried to burn it away, which made the inside black as opposed to the shining inside of the first can. So I took some aluminium foil, wrapped it inside the can and kept it on its place with some magnets.
For my large boiler of 80 L I got a large carton box and stuck some alu foil on the inside.
The original car window blanket is almost worn out, as the plastic inside seems to melt, but it still works.
Today I did a run and I could safely touch the outside (which is an extra plus!).
Now I think that reflection of the heat of the boiler is the main effect, rather than insulation.
A 50 % reduction seems large, but during the run I was thinking. The boiler has a temperature of about 90 dgr C, give or take 10 dgr. The blanket could be touched, so I guess about 30 or 35 dgr C. In an environment of 20 dgr C, the difference in gradient is large: about 70 dgr vs 15 dgr. As the heat loss is proportional to the temperature gradient, this simple and cheap insulation makes a large difference.
Your method makes better use of the applied heat, insulation diminishes the loss.
I must admit: I never tested it again on my copper boilers. But even a smaller effect makes it worth and, as I said, it is safe to touch the outside.
I made a close mantle of alu foil around my new glass Erlenmeyer but that made hardly a difference. Maybe I made it fit too close, without a layer of air.
Edit: Does this answer your question?